From A Wiki of Ice and Fire
Castamere is a ruined castle located near Tarbeck Hall and the Crag in the Westerlands. The former seat of House Reyne, Castamere contains gold mines. After the War of the Five Kings, it becomes the seat of House Spicer.
Following the failed Reyne-Tarbeck Rebellion, Tywin Lannister extinguished proud House Reyne and shattered their castle. The fate of the Reynes and Castamere is remembered in the song "The Rains of Castamere".