The Fortress of Green Isle was an old wooden castle, part of which hung over a lake. After being a home to the Otter Clans of Green Isle, it was inhabited by the wildcat Riggu Felis, and his army of cats. It was burned down after Tiria Wildlough and her companions defeated Riggu Felis and his army.
At first, Tiria lamented the loss, saying that castle would have been a good new home for the clans, but Leatho Shellhound told her the fortress stunk of cats and was better off burned to ashes, as a warning to any foebeasts.
The cat soldiers lived in the barracks and the otter slaves lived in the slave compound.
The Fortress appears in High Rhulain.