GTA V Mount Chiliad © Rockstar Games

There's something underneath Mount Chiliad, the mountain that towers above Grand Theft Auto V's vast map. Gamers already know what it is - based on the mysterious map found on its summit, it appears to be a jetpack, a hidden accessory in previous instalments of the game. Yeah, a jetpack.

Chiliad Snapmatic © Rockstar Games

How to get it though is another matter entirely, and one that's stumped the gaming hive mind. Whole online communities have formed around the hunt, and they’ve tried everything to find it, from dressing all three of the main characters up in robes to dropping tanks on the game’s secret flying saucers with a chopper.

Meanwhile Rockstar, a studio known for burying devious extras within its huge open-world games, is staying quiet, and a spokesperson declined to comment when we asked about the mystery. It's just one of gaming's truly evil easter eggs, hidden secrets that are meant to delight, but only frustrate instead: here are the most fiendish unlockables from the archive.

Fez and the uncrackable code

Phil Fish’s Fez is a puzzle game every bit as difficult as it is beautiful - and that’s just if you play through the game’s main story. To achieve 209.3 percent completion though (Yes, it’s possible) and unlock the mystery of the ominous black monolith in a hidden chamber didn’t just require some clever logic solving. It required you to know one of the developers and persuade them to reveal its secret.

That’s what designer Trey Reyher did , and it was only with his hints that other gamers managed to unlock it - even then they had to brute force solve it, teaming up to try every possible combination of letters, manually inputting them all for days on end. Their reward? The third piece of a red heart cube. Wow. Thanks, Phil.

Grand Theft Auto V - What’s in the hatch?

Swim to the bottom of the ocean in Grand Theft Auto V and you might just come across this curious hatch, with a light that flashes the message “Hey, you never call, how d'you fancy going bowling?” in Morse code. Is it part of the Mount Chiliad Mystery? Is it just a frustrating JJ Abrams reference? Is there a secret passage to the jetpack underneath? Nobody knows: get too near and you’ll get crushed by water pressure.

Zelda and the revenge of the chickens

Nintendo's Legend of Zelda series is one of the longest running series in gaming history, and not without a few of its own running jokes and easter eggs. One of the most memorable is its inclusion of chickens, that well, go get their boys for back up. Known as Cuccos, they were first found in the SNES classic A Link to the Past and introduced the revenge squad behavior - attack one for a period of time, and a whole indestructible flock would come back and attack you. Who said Ganon was hard?

Banjo-Kazooie’s sequel secrets

Banjo ice key © Gamerscore Blog/flickr

Complete N64 platformer Banjo-Kazooie with 100 percent and you’ll be given the locations to two Mystery Eggs and an Ice Key, all three of which are maddeningly out of reach. You just can’t get to them.

Supposedly, you had to buy sequel Banjo-Tooie to grab them, by swapping the cartridges in the console while the game was running. It was only after the sequel’s release however that hackers found the areas were accessible in the first game after all - you just needed to know the codes that developer Rare never thought fit to mention existed. Nice.

Donkey Kong and the hidden initials

One of the earliest arcade hits also hides one of the most elaborate time sinks in gaming history. If you’re able to set a new high score of more than 33,000 but less than 33,900 and then kill yourself off in a certain way, then wait several minutes, you’ll see the initials LMD appear on the start screen, a bonus buried in the code by programmer Landon M Dyer. A great pay off for all those quarters wasted, we think you’ll agree.

Diablo II’s bovine hell

Just like the chickens of Hyrule, the cows of Tristram get their revenge if you maltreat them. Complete the game, cast a few spells in the right places and you can enter the ominously named ‘Secret Cow Level’, in which vicious, bipedal cows will attempt to slaughter you and/or make you bow down before the sinister Cow King.

Prolonging the misery of Contra with the Konami code

Widely recognized as the hardest game of all time, run and gun shooter Contra’s secret doesn’t really help you as such. Punching in the infamous Konami code (Up, up, down, down, left, right, left, right, B, A and Start) grants you thirty extra lives, sure, but all that does is make the pain last longer. You’ll still hit game over, and end up hurling your NES controller at the wall. Unless you’re the guy in the video above, in which case, congratulations on your flawless run.

Stuck in an infinite loop on Starfox

There’s a hidden black hole level in this SNES classic, but that’s not the only secret mission. Fly through a giant space bird in the Hard Asteroid Belt (Yeah, bear with us) and you’ll end up in a bizarre alternate, wobbling reality where planets have faces and a giant floating slot machine attacks you. Hit three 7s on it and you’ll get the end credits at turbo speed, and then find yourself stuck in an infinite loop, where dying will only restart the level. Helpful.

The seven mysterious elevators in Grand Theft Auto III

Near Liberty City’s Portland Bridge, you’ll find a mysterious building with seven elevators, each wide enough to fit a car in. Weird. But get this: there are seven gangs within the game. Coincidence, or something more sinister? Nope, just coincidence. At the time of the game’s release in 2001, fans spent hours loading them up with every car in the game, in every possible combination in a futile bid to unlock some form of supercar, UFO, or anything in between. An easter egg Rockstar never found time to finish, or just an exercise in cruelty? You decide.

Moving the truck in Pokemon...or not

So here’s a truck, hidden away on a rocky outcrop in the original Pokemon Red and Blue games. You can only get to it late on in the game after one of your little critters learns to swim. It’s just there. Parked up. Conspicuous.