Arch Tower House, tucked behind a high-walled garden on South Quay, is one of Douglas's more unusual small buildings, with a castellated exterior and an internal spiral staircase leading through a trap-door to a flat roof that gives an extensive view over the town. Despite local legends claiming greater antiquity, a legal document of June 1853 describes it as a 'newly erected, castellated dwelling house,' meaning it was likely built only shortly before that date, probably by Thomas Shimmin, from whose widow it passed to a Mr Perrie in 1860. It later belonged to Mrs Ann Perrie, a widow, and the modest scale of the house belies its architectural charm.