From A Wiki of Ice and Fire
|Casterly Rock |
Fortress, Regional Capitol
Casterly Rock by Feliche©.
|Location||the Westerlands, Westeros.|
|Government||House Lannister , Feudal Lord.|
|Religion||Faith of the Seven|
|Founded||Before the Age of Heroes.|
|Named for||House Casterly|
The fortress is carved out of a great stone hill and its natural defenses are further enhanced with walls and other structures, In fact, the Rock has never fallen. Legend says that Casterly Rock is named for the family that ruled it in the Age of Heroes, the Casterlys, who no longer exist. The Lannisters trace their rule over it back to the Lann the Clever who tricked the Casterlys out of their castle and claimed it for his own. After Harrenhal, the Rock is most likely the second-largest castle in the realm. 
Three key rooms within the Rock are the Golden Gallery, the Lion's Mouth and the Hall of Heroes, where the Lannisters and their close kin who have died valiantly are interred. From below the Rock thunder can be heard, where the sea comes in. There is a place called the Stone Garden within the castle.