Elder Isles

An archipelago located in the Atlantic Ocean, across the Cantabrian Gulf from Aquitaine and southwest of the British Isles. The whole archipelago was threatened by the titan Joald, who was kept quiet and motionless by the magician Murgen. Eventually, Joald could be contained no longer and the cataclysm caused by his awakening caused the Elder Isles to disappear entirely into the Atlantic Ocean

Name
The Elder Isles are sometimes simply called "Lyonesse" after the largest and most powerful kingdom.

Size
The Elder Isles consist of dozens of islands, ranging in size from Guig's Fang a small jut of black rock, to Hybras which is approximately the size of Ireland.