The Old Priory and St Illtyd's Church, with its leaning spire, are among the oldest and most interesting buildings on Caldey. The Priory was home to the Benedictine monks who lived on Caldey in medieval times. It is built in an elevated position, close to the island's natural water source, beside the present day farmyard. It is constructed from limestone and sandstone indigenous to the island. The monastic buildings have been unoccupied since the Dissolution of the Monasteries, but St Illtyd's church is still a consecrated Roman Catholic Church.