About 13km (8 miles) north of Cardiff is this imposing moated fortress built partly on the site of a Roman fort. It was constructed by Earl Gilbert de Clare, Lord of Glamorgan, as protection against invasion by the Welsh prince Llywelyn ap Gwynedd in the 13th century. The massive water defenses of the castle form the second-largest castle area in Britain. You will note the leaning tower as you approach the castle, a result of efforts by Cromwell to blow up the towers. Perhaps you'll see the castle ghost, the Green Lady. She is supposed to be the spirit of a French princess who loved a handsome Welsh prince. When her husband, the Norman lord of Caerphilly, learned of the matter, he sent her into exile, but her ghost is still supposed to be here, lamenting her lost love. There is no luxurious interior filled with fascinating paintings or antiques, but you should come here mainly to see the impressive layout of the castle, with its defenses and great gatehouse, along with a fortified dam separating the outer moat from the inner moat. Wander also into the Great Hall.