Mermaid's Palace
Palacio de la Sirena
Mermaid's Palace is a small islet off the coast of the Rejo, near the Isla de los Cerdos.
Despite the name, there is no record of any actual palace there: it is a minor rock whose weight in the story depends on who happens to hold it.
Chapter 1
A base for the ironborn
Books only
During the war told in A Feast for Crows, the ironborn seize the island in the same offensive that also brings them the Isla de los Cerdos and the Islote Cangrejo de Piedra.
From then on they hold it as one of their outposts along that coast.