Repton

About

Repton, the eponymous protagonist, walks around an underground maze in a quest to find all the diamonds (some being held in safes, their release being triggered by finding and collecting a key) within a time limit in each of several levels, while avoiding being trapped or killed by falling rocks and monsters hatched from eggs. The original Repton game was released in the summer of 1985 and has 12 levels, with passwords making it possible to jump directly to later levels. If passwords were used though, on completion of the final level, the displayed message challenged the player to complete the game without using them.

Source: IGDB