From A Wiki of Ice and Fire
Horseshoe Rock is a small isle off the coast of the Arbor in the Reach.
A Feast for Crows
Horseshoe Rock is attacked by the ironborn, along with the Stonecrab Cay, the Isle of Pigs, Mermaid's Palace and Bastard's Cradle. Parts of it are now used as an ironborn base in the Reach.
- ↑ 1.0 1.1 A Feast for Crows, Chapter 45, Samwell V.