Gainsborough Castle is an 11th century earthwork motte and baileys fortress, founded by Roger de Poitou. The castle is built in the Norman layout, of two baileys with the motte in-between and encased by deep, wide ditches, with counterscarp banks. The low motte stands against an escarpment and is protected by a D-shaped bailey to the north and a large outer bailey to the south and east. With the dense cover of trees, the site is best viewed in winter. A mile south is Gainsborough Old Hall and 8 miles south-west is Hayton Castle.