Rothesay Castle is a ruined castle in Rothesay, the principal town on the Isle of Bute, in western Scotland. Located at NS086646, the castle has been described as "one of the most remarkable in Scotland", for its long history dating back to the beginning of the 13th century, and its unusual circular plan.The castle comprises a huge curtain wall, strengthened by four round towers, together with a 16th-century forework, the whole surrounded by a broad moat.