City of Saints and Madmen by Jeff VanderMeer

In the city of Ambergris, a would-be suitor discovers a sunlit street can become a killing ground in the blink of an eye. An artist receives an invitation to a beheading and finds himself enchanted. And a patient in a mental institution is convinced he’s imagined a city called Ambergris, invented its every last detail, and that he’s really from a place called Chicago.

Ambergris is a cruelly beautiful metropolis – a haven for artists and thieves, for composers and murderers. And once there, anything can happen. These tales of Ambergris include the World Fantasy Award-winning novella, The Transformation of Martin Lake.