Greenstone

Greenstone is a castle in the Stormlands. It is the seat of House Estermont, a vassal sworn to House Baratheon of Storm's End.

In the books
In the A Song of Ice and Fire novels, Greenstone is the seat of House Estermont. King Robert I Baratheon along with Queen Cersei Lannister and some of the court from King's Landing, including Ser Jaime Lannister of the Kingsguard, spent a fortnight at Greenstone. Robert cheated on Cersei with a cousin of his and Cersei believes that it was there that she and Jaime conceived their eldest child Joffrey Baratheon. Jaime called the castle Greenshit.