Butron Castle, Basque Country, Spain. This castle is the world's largest existing medieval castle in the world. It fell into disuse and was later renovated and opened to the public. This proved to be unsuccessful and the building was closed to visitors although the grounds remained open. In November 2005 the building was purchased by INBISA (Grupo Empresarial) for 1,629,743 euros but it remains under the general protection of Spanish law 16/1985 in respect of historic buildings in Spain.