Labyrinth Hero deploys miniature dungeons to explore, each level populated by a couple of monsters, a treasure chest, a button and an exit triggered by said button.
It's super easy to play, too, requiring little more than pointing your mouse where you want your hero to move. Everything else is automatic. Occasionally you'll get a Yes/No choice - written in Japanese - but there's no reason why you wouldn't click Yes.
How many levels can you get through this lunchtime?
Labyrinth Hero [Skipmore]