The Shadow Fold, also known as "the Unsea" or simply the Fold, is a swath of darkness that suddenly appeared one day. It is a section of nearly impenetrable darkness that grows every year and contains volcra among other unnamed horrors. It was created by a powerful Grisha known as the Black Heretic. The Shadow Fold cuts directly across the Vy, a wide road that once stretched across the land connecting Os Alta to the port cities on Ravka's western coast. On maps, the Shadow Fold is shown as a long, narrow lake, a stain, and sometimes just a shapeless cloud. People who need to travel across the Shadow Fold, or Unsea, use a skiff, a ship-like transport that sails across the sand.
The Shadow Fold is first mentioned when Alina Starkov and Malyen Oretsev have to go through it with their regiment.