The Shadow Fold, also known as "the Unsea" or simply the Fold, was a swath of darkness that split the eastern and western sides of Ravka in half. It was destroyed by Alina Starkov during the Ravkan Civil War. Before its destruction, the only reliable way across it was with a Sandskiff.
The Shadow Fold was a section of nearly impenetrable darkness that grew every year and contained volcra among other unnamed horrors. The Shadow Fold cut 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 was shown as a long, narrow lake, a stain, and sometimes just a shapeless cloud.
The Shadow Fold was created hundreds of years before the events of Shadow and Bone by The Darkling because of his want for power.
The Shadow Fold was first mentioned when Alina Starkov and Malyen Oretsev had to go through it with their regiment.