Many of the most awe-inspiring caves formed along the shores of oceans and lakes. Also known as littoral caves, these geological wonders are carved into rocky coastal cliffs through long-term wave action along weakened fault lines in cliffs. In addition to spelunking, sea caves provide ample recreational opportunities for kayaking, swimming, free diving, scuba diving and more. While many of these caves are found in the craggy coastlines of Europe, some of the largest sea caves in the world — such as California's Painted Cave and Oregon's Sea Lion Cave — can be found on the rocky Pacific coast of the United States. Here are just 9 of these extraordinary watery wonders.

1 of 9 Fingal's Cave Columnar jointed volcanics of Fingal's Cave. (Photo: Steve Allen/Shutterstock) Located on the island of Staffa, Scotland, Fingal's Cave, also known as "Uamh-Binn" in Gaelic (meaning "cave of melody"), is well-known for its arching, cathedral-like geological features and emanating eerie sounds. The cave, along with the entire island of Staffa, is composed entirely of hexagonal basalt columns (similar to Northern Ireland's Giant's Causeway), which produces the naturally arched ceiling. The easiest way to see this awe-inspiring cave for yourself is to take a sightseeing cruise from the town of Mull. The cruises land close to the cave, and the hexagonal basalt columns serve as perfect stepping stones to walk along the shore and enter the cave.

2 of 9 Sea Lion Cave Photo: Paul Hamilton /flickr Oregon's Sea Lion Cave is not only famous for being the largest sea cave in the world, but also for the plethora of barking wild sea lions that lounge on its craggy rocks. Located just a few miles from Florence, this enormous basaltic cave is situated 300 feet beneath Highway 101. To reach the inner caverns, visitors must take an equally deep elevator and then proceed down some stairways and trails.

3 of 9 Alofaaga Blowholes Photo: ...your local connection /flickr One of the most exciting and magnificent natural attractions in the small island country of Samoa are the Alofaaga Blowholes. When high tide rolls in, powerful waves are jettisoned up through a series of tubes created from lava flows, causing a watery explosion similar to that of a massive fountain or geyser. This definitely isn't a cave for spelunking, however; the breaking water that splashes through the high pressure tubes would easily kill anybody who was unlucky enough to fall through the holes. This lethal force is often demonstrated on a smaller scale by the locals in the area, who will throw coconuts, rocks and other objects into the holes just as they are about to blow (see video).

4 of 9 Great Blue Hole Photo: Wollertz/Shutterstock Nestled in the Lighthouse Reef Atoll of Belize is the Great Blue Hole, a large submarine vertical cave that measures 984 feet in diameter and 407 feet deep. With its beautiful, clear water and the variety of wild marine life residing in its depths, the enormous blue hole is a popular scuba diving destination. Today's blue holes, which are found all across the world, were formed from erosion during previous ice ages when the Earth's sea level was significantly lower than it is now. Although the Great Blue Hole is most definitely great, it is not the deepest. That title is held by Dean's Blue Hole, located in the Bahamas, with a depth of 663 feet. For a demonstration on the magnitude of its size, check out Guillaume Nery, world champion freediver, as he does a freefall dive inside the hole in this video clip shot by fellow freediving champion, Julie Gautier.

5 of 9 Blue Grotto Photo: Gimas/Shutterstock With its gorgeous blue water, Blue Grotto is one of the most well-known sea caves in the world. It is located off the coast of the island of Capri, Italy. Guided boat tours are readily available so you can witness the cave for yourself. The opening to the cave is so small that passengers must lie down on the boat as the guide pulls the boat inside. As a result, inclement weather and high waves can thwart attempts to see the cave.

6 of 9 Painted Cave Photo: Mike Baird /flickr The second longest sea cave in the world is Santa Cruz Island's Painted Cave off the coast of California. Formed along a fault line, the length of the cave measures in at 1227 feet, and the entrance is 130 feet high. The Painted Cave was named for the colorful rocks, lichen and algae featured within the cave. In the spring, a waterfall cascades down in front of the entrance. One of the most common ways to experience this exquisite cave is to take a boat ride to the island and then explore the watery cavern via kayak.

7 of 9 Apostle Islands Ice Caves Photo: critterbiz/Shutterstock For a truly unique caving experience, go no further than the shorelines of Apostle Islands in Wisconsin's Lake Superior. In the summer, kayaking along the shore enables visitors to observe each exquisite cavern. When the lake freezes over in the winter, the caves follow suit. Visitors trade in their kayaks for rugged snow boots, and trek off on foot to see frozen waterfalls and enormous icicles. Apostle Islands National Lakeshore isn't known for more than its striking caves; the lakeshore's ecosystem is one of kind. Numerous species of plants and wildlife call these islands home, including a large concentration of black bears on Stockton Island and many nesting birds. To see what the caves look like in the summer, check out the following video:

8 of 9 Smoo Cave Photo: Jaroslav Sekeres/Shutterstock Located near the village of Durness, Scotland, is Smoo Cave. This impressive geological wonder was carved into limestone by the Allt Smoo, a river that runs above and pours into the cavern through a sinkhole. This water cave includes both sea water and fresh water. While the inner chambers were formed by the Alt Smoo, the first chamber, which features a easily accessible and expansive cave mouth, was formed by sea water erosion. The cave is fairly easy to access, and there are stairs, walkways and restrooms available for the nearly 40,000 people who visit each year. Boat rides are offered within the inner watery caverns during the summer.