Nicknamed the “Castle in the Sea,” this stone tower sits on a rock in the sheltered harbor of Castlebay—the largest town on the Isle of Barra. In fact, you need to take a small boat across the bay to visit Castle Kisimul, which serves as the seat of the chief of Clan MacNeil. The only significant medieval castle to survive in the Western Isles, it features a curtain wall enclosing a central courtyard, and stone spiral stairs that lead to a great hall where worthies once dined. When visiting, be sure to climb up to the tower house battlements for panoramic views of Castle Bay.