Sometimes the simple games are the best.
Crypt raider pits you against all manner of puzzles and monsters to explore the Crypt and hopefully find the treasure. It is a bit of a homage to the Indiana Jones era, and integrates this into a Boulder Dash-inspired puzzler.
With 100 levels of puzzles to solve in the full game, this should keep you occupied without straining the brain too much. Your task on each level is to move a jewel towards the exit, tackling the numerous obstacles in your path.
This download includes seven of these levels, with the other 93 levels being playable online only.
It might be a simple game, but it will keep you entertained for hours. There is no Save Game option, but each level has a code - simply jot this down to begin again where you left off.