Casterly Rock is the ancestral stronghold of House Lannister. It is located on the Western coast of Westeros on a rocky promontory overlooking the Sunset Sea. It overlooks the major city of Lannisport. A major goldmine is located under Casterly Rock. It is one of the most productive in the realm and provides House Lannister with their wealth.[1]
According to tradition, the castle was originally held by the House Casterly, the old Kings of the Rock. They were hoodwinked into giving the Rock to Lann the Clever, a legendary trickster and ancestor of House Lannister, thousands of years ago, during the Age of Heroes.