When Isolde tells Tristan that he can wash himself in the ocean, she clearly means the sea, as the ocean is on the west side of Ireland, not the east. See more
Britain. The Dark Ages. / The Roman Empire has fallen / The land lies in ruins, divided among feuding tribes. / To the west, Ireland has flourished - untouched by the Romans, protected by the sea. / Led by their powerful and righteous king, the Irish have subdued the Britons... / Knowing that if Ireland is to prosper, the tribes must never be allowed to unite.