The hero of this game, Rockford, is a very cute fellow. He specialises in digging tunnels and collecting jewels. The snag is that the ground through which he burrows is littered with boulders, which drop into the tunnels and squash him if he's not careful.
There are 16 sizeable caves for Rockford to dig his way through, you can choose to start at the first, fifth, ninth or thirteenth, so even if you're hopeless at the game, you can get to see quite a few different screens. Each cave has different problems; some are relatively straightforward, while in others the jewels are guarded, or have to be created by strategically dropping boulders onto assorted obstacles.
The graphics are adequate rather than stunning. The weakest point is that the screen scrolls rather slowly. If you move too fast, it is possible to lose sight of Rockford off the edge of the screen, where he can run into unseen hazards.
It's a game with lasting appeal, needing careful planning as well as fast reactions, and is well worth adding to your calculations.