C.
Your quest is to find the legendary treasure, the Orbs of Yendor. HyperRogue can be played for free from its website. The twist is the unique, unusual geometry of the world: it is one of just few games which takes place on the hyperbolic plane. Witness a grid composed of hexagons and heptagons, straight lines which seem to be parallel, but then they diverge and never cross, triangles whose angles add up to less than 180 degrees, how extremely unlikely is it to reach the same place twice, and how the world seems to be rotated when you do return.