A huge horned turtle, one of the Old Men of the River, which Yandry
believes is the Old Man of the River
Art by Puppy-Chow.
The Old Men of the River are a species of gigantic turtle that live in the river Rhoyne. They are held sacred by the Rhoynar as the consorts of Mother Rhoyne.
According to legend, the first of the Rhoynish Wars, the First Turtle War, began when Valyrians killed one of these gigantic turtles.
A Dance with Dragons
When the Shy Maid sails down the Rhoyne at Ny Sar, they see an exceptionally huge horned turtle, which comes to the surface and bellows at them. Ysilla says they are blessed to see it, and Yandry declares it to be the Old Man of the River, not just any turtle but an actual god.
Tyrion Lannister sees a large turtle shell, painted in different colors, decorating a stone inn at Selhorys.