Sea of Dorne
From A Wiki of Ice and Fire
The Sea of Dorne is a large sea on the eastern side of Westeros. It is bordered to the north by Cape Wrath in the Stormlands, to the west and south by Dorne, and to the east by the narrow sea. The river Wyl flows into the sea.
Settlements along the Sea of Dorne include Ghost Hill, the Tor, Yronwood, Wyl, Stonehelm, and the Weeping Tower. Within the sea sits an old castle on a rock, Ghaston Grey, which is used as a prison for criminals by House Martell.