Storm's End is surrounded by a massive outer curtain wall, one hundred feet high and forty feet thick on its thinnest side and nearly eighty feet thick on its seaward side. It is composed of a double course of pale grey stone with an inner core of sand and rubble. The wall is smooth and curving, the stones so well placed and so perfectly together that the wind can find no purchase. Storm's End has only one tower, a colossal drum crowned with formidable battlements, so that from a distance enemies can see what appears to be a single huge, spiked fist thrusting towards the sky in defiance. The tower is so large that it comfortably contains the granary, barracks, armory, feast hall, and lord's chambers all at once. There is a watery passage through a cavern that leads beneath the castle, protected by a portcullis, bars, and murder holes.