MineCave is a game I wrote in BASIC on a real Commodore 64. The game is the result of a challenge I did for RetroGameCouch.com.
In the game, which is entirely in text-mode, you mine a mining claim for ores. These ores need to be sold at the shop to earn cash. Cash is used to upgrade your tools to be able to access lower parts of the claim.
You do however also have to keep track of your health and oxygen levels.
On the bottom of the mine lies a big red diamond. This is the stone you are after. Reach it and you win the game.