What are some of the scariest things you can think of, that would make a landscape?
Mesas surrounded by lava pools?
Carnivorous plants that will eat humans?
Cacti with poisonous spines that can be fired like darts at potential victims?
Man-eating beasts e.g. dragons.
Zombies roaming the landscape, seeking souls to join the ranks of the undead?
Or you might have something much more plausible:
A city watched over by a dictatorial government (George Orwell's 1984).
America w/o the Bill of Rights?
All of these are examples that you could use as a 'nightmare lanscape' and then all you have to do is include descriptions e.g. "The air always reeks of brimstone," "The hidden eye sees everything," "Always looking over my shoulder for the Gestapo," or "the shield rang as the poisonous spines hit."