Palimpsest by Catherynne M. Valente

The book is a richly woven tale that follows four strangers who find themselves linked by a dream-city named Palimpsest, which they can only access through their sleep. Each of them is marked by a map of the city on their skin, a living remnant of their nocturnal visits. To return to the city, they must engage in intimate acts with other strangers bearing the map. As they navigate their lives in the waking world and the enigmatic streets of Palimpsest, they are drawn deeper into the city's mysteries and must confront their own desires and heartaches, while the fate of this otherworldly place becomes increasingly intertwined with their personal transformations. The 12174th greatest book of all time