A British platform game that came quite late in the life of the Atari 8-bit computers (released by Zeppelin Games in 1990), Cavernia is a fairly simple left to right run-and-jump-a-thon but with nice presentation and decent controls.
You control a small kid (called Teddy Arklethorpe) who’s dressed in an adventuring outfit (complete with pith helmet) and who must collect items to reveal the key to the exit door. Touching something dangerous or falling too far loses a life, but you at least keep all the items collected on a level to that point, so don’t have to start from the scratch.
The first level is a cinch, the second level more challenging, and the third level is quite hard. So quite a steep difficulty curve. There are 16 levels in total.
More: Cavernia on Atari Mania