Spelunky is a 2D survival platformer that started as a web game and eventually became PC Gamers game of the year in 2013. The game is now available on Steam, PSN, and XBLA. Technically that game is an HD upgrade from the original but isn’t free. Luckily the original is still 100% free and can be played from a browser or even downloaded. As the name suggests, the game is about spelunking, or cave diving. You play as a cave explorer in search of treasures while trying to survive the dangers around every corner. With snakes, bats, and spikes coming out of the walls, the game is just as much about surviving as it is about finding some sweet loot. As far as web games go, Spelunky has a good amount of depth and replayability. Dying might come with some significant consequences but the game play will have you coming back over and over again to kill some time.
You can play the web version HERE
If you want to download the game onto your pc you can do that HERE.
Enjoy and happy Spelunking!!