After my recent popular post on 104 things to do during a money-free weekend, I received a most interesting comment from a Lifehacker reader named HFC:

It looks like a lot of free things are boring and/or require you to actually have friends. Aren't there any fun things I can do by myself?

This comment really spurred my thinking. I'm a proud introvert - most of the activities I enjoy are either done alone or with a very tight group of friends. I don't feel comfortable in large social situations, though I've learned how to cope well with them and not come off as a deeply antisocial jerk.

The only problem is that a lot of activities that you can do yourself require some money to enjoy. Renting a video costs money. Playing a video game? Very expensive.

Here are 50 suggestions for free or extremely cheap ways to spend your time. Some of these have appeared on other lists of free stuff to do before - others are new to this one. Similarly, some of these may appeal to you - others may not.

If you're an introvert, have fun and save some money!

1. Make a collage postcard for PostSecret. For those unaware, PostSecret is a website to which people send postcards telling their deepest, darkest secret anonymously; the blog creator then posts images of some of those postcards on the blog. All you need is a blank postcard, some imagination, and a secret to tell. Look around your house for the materials you'll need - old magazines are always a great place to start harvesting materials from. Look for images that reflect the secret you want to tell, then make a collage out of them on the card. Whether you mail it or not is up to you, but it's a wonderful way to get creative and get some release on a secret you've been hiding.

2. Try out parkour. Parkour is essentially an obstacle-course style athletic activity where you try to find the quickest path from point A to point B. You can do this pretty much anywhere - your yard, the park, anywhere in a city - and it's always a lot of fun and good exercise. Plus, it's an incredibly effective way to improve your mind-body coordination, as practicing this regularly will improve your balance and also your quick-decision skills.

3. Master a Rubik's Cube. There are few parlor tricks that are more entertaining (for me, at least) than watching someone solve a Rubik's Cube quickly. You can easily get ahold of one of these (ask on Freecycle or Craigslist) - the trick is figuring out how to solve it on your own, then how to solve it quickly. Here's a great guide for solving a Rubik's Cube.

4. Make a list of all the people who were a positive influence on your life and write each of them a thank-you letter. Think for a bit about all of the people who have inspired you and helped you along in your current life path. Make a list of all of these people - mine, for example, includes my high school English teacher, some relatives and friends, and a few college professors. Then pull out some paper and a pen and write each of them a handwritten letter, reminding them of how they helped you out and thanking them for doing so. It's a great way to get in touch with the people who helped shape your life, and it's something you'll feel genuinely good about for a long time.

Related: Planting Seeds for the Future

5. Learn how to make string figures. I love making string figures. All you really need is a big loop of string and some imagination. Figuring out how to loop string around your fingers to make visual compositions of all sorts of things is a lot of fun. You can easily make spider webs, bridges, and other interesting things. Even better, learn about some of the cultural heritage of these string figures and try to relate the stories yourself as you make the figures. Here's a guide to the basics.

6. Learn some basic yoga poses. Yoga is a great way to relax and meditate while stretching the muscles of your body and getting a surprisingly intense workout at the same time. Basic yoga is extremely simple and feels really good - a stretching routine once a day feels really good to me. Here's a great introductory video to the very basics of yoga.

7. Take a free online class to learn the basics of a new topic. We're living in a golden age of free education, with online college courses available from some of the best academic institutions in the world like MIT, Stanford, and Harvard. I recently shared 10 of the best online classes I've taken for free over the past few years, in subjects varying from computer science to music theory to philosophy. You can even learn in-demand job skills like computer programming for free.

8. Teach yourself how to cook. Not only is cooking the most cost-effective way to provide sustenance for yourself, it's also an art form that rewards experimentation and practice. Challenge yourself to assemble an interesting meal out of the materials you have on hand. You might just find that it's fun, that you've learned something new, and you've created something tasty to eat for just pennies. Here are a few tips if you're new to cooking at home.

9. Take a walk in the park. Likely, there's either a park or a secluded rural area within walking distance of where you live. Set out on foot to go there, then just wander around enjoying what you can observe and take in. Enjoy the natural beauty around you. Even better, find a nice secluded place and engage in another of the activities on this list in a wonderful natural environment.

10. Listen to a podcast. Podcasts are wonderful snippets of intelligent (mostly) and engaging talk radio, where people pour out their hearts and ideas for you to hear - for free. Here are 10 podcasts I quite enjoy to get you started: The Splendid Table (on food topics), Marketplace (on economics and business), Speaking of Faith (on religion), Fresh Air (interviews of general interest), This American Life (quirky general interest stuff), This Week in Tech (technology news), Car Talk (automotive news and tips), Keith and the Girl (pop culture), Free Talk Live (non-partisan politics), and Nobody Likes Onions (comedy).

11. Learn a simple papercraft. Papercraft includes everything from origami (and neat things like paper snowflakes) to full paper models of ... well, anything. The excellent OrigamiVideo.net has a huge collection of videos on how to get started making almost anything origami (and many other papercraft projects, too).

12. Do a crossword or a sudoku puzzle. Paper-and-pencil puzzles are a great way to stretch your mind in new directions. You can easily get them for free - the New York Times gives out a free crossword each day, while an excellent free British-style cryptic crossword from The Herald or a huge number of free sudoku puzzles at WebSudoku should provide you with more than enough puzzle-solving pleasure for a long time.

13. Teach yourself solitaire (or a solitaire variant). All you need is a deck of cards, a logical mind, and plenty of spare time. Klondike is the most well known one, but there are a lot of fun solitaire games out there: Freecell, Golf, Patience, and Beleaguered Castle. There are many others - here's a sampling of ones to try.

14. Put some positive affirmations around you. On a series of Post-It notes, write down 10 or so positive things about yourself (I find writing down positive memories is a great way to go, ones that put a smile on my face), then put them in places where you go irregularly and post them, like a rarely-used supply closet or the inside of your car's trunk. Then, when you find them, they'll lift you in a positive way. You could also do the same thing for someone you care about, posting some little reminders of their best qualities in places where they'll discover them later.

15. Start a blog on a topic that fascinates you. If there's a topic that fills you with passion, consider starting a blog on that topic. It's easy (and free) to get started at Blogger or WordPress. Whenever you have an interesting idea about your topic or just get a strong desire to explain the basics, write it all out and post it there. It's a great way to organize your thoughts and channel your passion on a particular topic.

16. Watch an old movie from your collection. Almost everyone has some old movies lying around. Dig some out and watch them. I find it particularly enjoyable to watch old home movies - videos of when my son was a newborn, for example, are particularly fun to pull out. I also enjoy watching movies that I dearly loved 10 years ago but haven't watched in years - I now see many of them as goofy fun for a rainy afternoon.

17. Teach yourself a card trick. Card tricks are a particularly fun way to entertain people in almost any situation, and there are as many different card tricks as there are grains of sand on the beach. Pick up a deck of cards and invest the time to learn one cold so that if the opportunity ever offers itself, you can easily show off that trick. For starters, here's how to do a clever and simple trick called Quick as a Wink.

18. Tour your neighborhood on foot. Most neighborhoods have many interesting secrets and things to enjoy and observe on foot. Just head out of your front door and wander wherever your spirit takes you. You'll likely find all sorts of interesting things on your journey - places you didn't know about before, interesting landmarks, beautiful sights, and perhaps an interesting free thing to pick up along the way.

19. Go stargazing. The stars in the night sky are one of the biggest reasons I love living in rural Iowa. I can look skyward any non-cloudy evening and see a sky full of stars. If you're lucky enough to live in an area with a clear sky. spend an evening or two gazing at the stars. In particular, try to go outside on nights where a meteor shower is in progress, as that just adds to the beauty of the Milky Way. Download a free app like SkyView Lite (for iOS or Android) to help you pick out constellations, planets, and even passing satellites in the night sky above you.

20. Get your finances in order. While this might not seem like fun at first glance, having a financial plan can greatly reduce the stress of day-to-day life and also greatly increase your peace of mind. Spend some time reading up on personal finance, working through activities like 31 Days to Financial Independence, setting goals, understanding your current financial state, doing estate planning, defining a budget, and so on. It's all worthwhile, all free, and all of it will add to your peace of mind.

21. Make a time capsule. Find an old shoebox, then go around your home and find items that clearly mark the reality of your day to day life - a newspaper, receipts, your child's recent drawings, magazines, photos, and so on. You can record a family video on your smartphone and copy it to a UBS drive and include that, too. Put them in the box and when it's got plenty of items in it, tape it up very securely and write a date in the future when you can open it - say, in 10 or 15 years. Not only is it fun to collect the items now, it can be really interesting to look through those items in the future, when not only your life has changed, but cultural touchstones have changed as well.

22. Find (and read) some free, alternative newspapers in your area. Most urban areas have a handful of free newspapers, supported entirely by advertising or by sponsorship, that often provide insightful and interesting reading. Look for ones in your area in the lobby of the local library, in the lobby of grocery stores, and at city hall. Collect them, then take them home for a nice reading. In my area, I have easy access to Toons (a collection of political cartoons), The Sun (community events), Cityview (an independent public affairs paper for Des Moines), and Juice (a twenty-something paper in Des Moines published by the Des Moines Register). All of these can provide worthwhile reading - and they're all free.

23. Learn a musical instrument. This might not strike you as a free thing to do, but it's actually surprisingly easy to learn how to play an instrument for free. You can often get basic instruments (keyboards, acoustic guitars, and sometimes other things) on Freecycle or Craigslist, plus there are countless opportunities online for basic lessons on how to play any number of instruments, as well as how to read music. All it takes to get started is some time and some interest.

24. Listen to your favorite music up loud (and let yourself dance to it). I love to turn the music up loud on occasion and bounce around to it (all in complete privacy, of course). Few things get me more pumped up than a really lively song and a bunch of moving around in rhythm to the music. For me personally, few songs get me bouncing around energetically more than AC/DC's Let There Be Rock. But that's just me - I'm sure you have your own favorites.

25. Visit the library. This one's right in the middle of the list, but it's one of the best free things for an introvert to do on the cheap. Your public library is a gigantic collection of free books, movies, music, magazines, and countless other things - all there for the borrowing. Plus, there's usually a lot of activities there for the introvert, from film showings to recommended reading lists and community calendars. Stop by and see what things a library really has to offer.

26. Do a jigsaw puzzle. A jigsaw puzzle is a wonderful engrossing activity. My family used to traditionally cover the kitchen table with jigsaw puzzles for much of the winter, with everyone sharing in the puzzle-solving process. You can usually find them for free on Freecycle without any effort at all and they'll give you many hours of solitary enjoyment.

27. Build a detailed family tree. Most people are aware of at least a couple generations of their lineage, but things often get confused when you get further back than that. Spend some time building a detailed family tree, starting with what you know and eventually adding your own research to the mix. Contact older relatives for assistance, then use resources like Ancestry.com to fill in more blanks. Add as much detail as you'd like or, even better, make it into a multimedia project on your computer, with pictures and other materials.

28. Teach yourself to meditate. For stress relief and aid for overcoming tiredness, few things work better for me than a short period of meditation. The easiest technique is to just sit in a comfortable chair, close your eyes, and focus on nothing but breathing slowly for a while. Breathe in slowly, hold it for a bit, breathe out slowly. Over and over. I've been practicing meditation for at least 10 minutes a day, and the effects have been profound.

29. Read a book on your shelf that's unread. Most of us have a book or two around our home that we haven't read - something we keep meaning to read "someday." Let today be that someday. Dig out that book and give it a serious, long reading. Let yourself get lost in the book, no matter what it is, and see if you can get through it (or at least a significant portion of it) in one sitting. Getting lost in a book is one of my favorite experiences - and it can easily be a free one.

30. Start a workout program at home. A basic workout program doesn't need to involve an expensive gym membership - it just needs to involve personal initiative. After all, many of the most effective exercises -- running, walking, sit-ups, prone lifts, push ups, jumping jacks -- don't involve any exercise equipment at all. Before you get started, make sure you're in good health with a doctor's visit. Then string some of these free exercises into an at-home workout routine, or try some of the the ever-changing free daily workouts at Darebee.

31. Do a "Wikipedia walk." I often burn a good hour doing a "Wikipedia walk" as I investigate a particular topic and find interesting connections to other areas of personal interest. All you have to do is think of a very broad topic you're interested in - say, philosophy - and read through that entry, following any and all links that are of interest. What I usually do is open up a bunch of new browser tabs from links on that first entry, then read each tab, opening new ones, until I've had my fill. It's a great way to learn the details of any topic, from knitting to the Eastern Orthodox Church.

32. Start a natural collection or sketchbook. All that's required to start a natural collection - or a notebook that collects observations - is an interest and a willingness to investigate. Like rocks? Start collecting and identifying particular samples. Birds? Make some sketches or take some photographs. There's no limit to what you can observe and record in the natural world. You can observe people, too, or automobiles - the possibilities are endless. Here are some tips for getting started with a natural collection.

33. Organize your collection(s). Speaking of collections, one wonderful solitary activity is organizing your currently-existing collections. Go through your collection of CDs, DVDs, trading cards, books, political buttons, or whatever item you collect and put them in a reasonable order. Along the way, you'll find all sorts of little things to do to pique your interest, simply from your personal enjoyment of the things you've collected.

34. Learn how to juggle. Juggling is a really enjoyable pastime: it teaches hand-eye coordination and dexterity while simultaneously being quite soothing. It's also quite simple - you just need three balls to learn how to do it. Here's an excellent tutorial video on how to juggle.

35. Play a free online game. There are countless sources of excellent online games - try Kongregate for starters. Lately, I've been playing "Ticket to Ride: Europe" online using the free trial - it's one of my favorite board games and it's a blast to play whenever I like.

36. Seek out a solitary place on foot. One activity I particularly enjoyed doing during my college days was exploring seemingly crowded places but searching for nooks and crannies that were completely isolated from the hubbub. I used to find small back rooms of the large university library and just curl up in there and read. I also used to climb the large trees on campus to get up above the crowds below. The search for solitude was enjoyable and finding it was sublime.

37. Start (and maintain) a journal. I've been keeping a journal for years now and find it valuable and fulfilling. Just start on any old spare notebook you have lying around your house. Jot down the most interesting things you did that day - even if they don't seem interesting right now. Eventually, you'll start to build up a nice catalog of entries and it'll become quite fun to read earlier writings.

38. Go to a free movie. If you look around a bit, you can often find free movie showings in your community. Start by visiting the libraries available to you - many have open movie nights, where you can go sit in the library auditorium and enjoy a free film. If you live near a university, there's often a film group there showing a weekly movie as well. Often, other community groups will put on regular film nights as well - just check around.

39. Take up walking, jogging, or running. There are almost no solitary activities that combine physical exertion, rhythm, and peace of mind like sustained walking, jogging, or running, and all you really need to get started is a pair of decent shoes. Define a regular, sensible jogging routine (three times a week for 30 minutes is a good way to get started) and dig in on the paths around you. The key isn't to kill yourself, but to just exert yourself a little and figure out how to get into a good, healthy rhythm along the way. For a more rigorous, flexible free workout, try rucking - walking or hiking with extra weight in a backpack.

40. Take a long, hot bath. Just fill up your bathtub with some nice, warm water, get yourself in there, and kick back. Enjoy the long soak and just let the little worries drift away for a while. To me, this is almost as good as a professional massage but the cost is just right - plus it's just as convenient as the bathroom down the hall.

41. Rearrange (and thoroughly clean) a room. Sometimes all it really takes to make a place seem fresh and new is a thorough cleaning and a rearrangement of the decorations and furniture. Put some elbow grease to work in your favorite room in your home that's just a bit tired and see what you can do to make it smell and look fresh again. If it's a regular place where you spend time, just that little bit of change can make a world's worth of difference.

42. Write a poem. This is an activity that forces almost everyone to think a bit differently about the world around them, but from that experience can come much wisdom and growth. Try to express whatever you're feeling in your heart in words, in whatever form seems the most natural and appropriate. Then tease the words around a little - find ones that seem to click with how you feel. The entire process will leave you feeling interesting things - and often feeling deeply fulfilled.

43. Get politically informed. Find out what candidates are going to appear on your ballot in the upcoming election (as well as any ballot initiatives) and find out more about each one of them. Compare the candidates running for the same office and make a rational decision about each campaign. You can do most of this research online today - if you can't, call the local offices of each political party to find out about local candidates. Doing this will make you an informed voter and likely an influential one, since you can state clear reasons why you're supporting the candidates you're supporting and this can often sway others.

44. Take some digital photographs and share them online. If you're building a natural collection or observing anything interesting at all, take along your smartphone or camera and snap some photographs of it. Then, take these images and share them with others on a photo-sharing site like Flickr. Be sure to put in the effort to add detailed notes about each picture so that others may enjoy them as well.

45. Discover new music you might like. There are countless free online streaming services available to you that can help you find new music that matches your tastes. Sites like Pandora or Last.fm allow you to type in the name of a musical artist you like, and then get a customized radio station of nothing but similar artists, virtually ensuring you'll discover some compelling new music.

46. Create an interesting video and share it on YouTube. All this takes is a smartphone or digital camera capable of capturing video, some basic video editing software (there are free web-based programs online), and some creativity. Think of something interesting that you could make a compelling video about, create a tight script for that video, then go around collecting the shots you need. Once you're done, edit the video into a slick presentation and upload it to YouTube for the world to see. Keep it up, and you could potentially create a new income stream.

47. Enter a short story competition. Short stories are a lot of fun to write - in fact, writing them is my secret passion. Whenever I have spare time, I like to seek out short story competitions, write out stories for them, and then ... fail to actually enter because I'm too self-conscious about my short stories. But I still gain something big from it - the process of writing a short story is a lot of fun.

48. Dig deep into a blog. Got a blog you enjoy reading (like, say, this one)? Go waaaay back into the site's archives and read some of the older stuff. You'll often find that the writing has changed drastically since the early days and that you've missed out on a ton of interesting and compelling ideas. Look for an "archives" page -- you can dig through thousands of my past The Simple Dollar posts here.

49. Attend a free concert. Many communities offer free weekly municipal concerts in the park and larger cities often have multiple free concerts each day in various places. Pay attention to the community calendar and other resources and go by yourself to a concert. Live music can be a very compelling and exciting thing - don't miss out on an opportunity to enjoy it.

50. Watch a sunrise or sunset, from beginning to end.

This really says it all:

That picture depicts sunset over the Grand Canyon in July 2005 when I visited there with my wife. The amazing part of that scene is that you can enjoy much the same beauty anywhere you are, whether you're an early riser or a night owl. Just watch the sun rise and take on brightness, or watch her set and shed her colors. Beauty, indeed.