Attractions in Castle Cary include a small circular eighteenth-century prison called the roundhouse. This is a temporary prison, or village lock-up. It was built in 1779 by Mr WM Clark for £23, from money left to the poor of Castle Cary in 1605. The structure is circular, stone and has a domed roof. It is in diameter and high with two iron grills for ventilation. The building has an inner and outer door. The interior of the building has a single stone privy. In 1992, the Lord of the Manor, Sir Henry Hoare Bt., gave the building to the parish council.