Thunderfield Castle is either an earth ringwork and bailey fortress or the site of a medieval moated manor house, founded by the Clare family. Interestingly this site was greatly remodelled in the Victorian era, with alterations to the ditches and a system of pipes and valves installed for the supply of water. Guarding the oval platform are two wet ditches and to the north is a large bailey with a small D-shaped inner barbican, both with their own wet ditches. Excavations have also found evidence of a 13th century bloomery and with the dense cover of trees, the site is best viewed in the winter. 6 miles north is Reigate Castle and 14 miles east is Hever Castle.