Rhineland defense tower in Germany and purposely constructed with slanting and uneven walls, ceilings, and roofs. This unique structure sits on the south side of the island facing Alexandria Bay and boasts a two-lane bowling alley and stage for performances. The Alster Tower cafe is one of the restoration projects currently taking place on the island. The George C. Boldt Yacht House on nearby Wellesley Island represents the only remaining wooden yacht house structure of this kind. The interior features extensive living quarters and a number of antique and wooden boats. For an additional admission fee, visitors can take a shuttle from Heart Island to the Yacht House on Wellesley Island to tour these exhibits. It was listed on the National Register of Historic Places in 1978. The 1969 children's novel Secret Castle by Anne Colver is about the castle and Alexandria Bay. Gallery See also Calumet Island Castle Rest Dark Island Just Room Enough Island References Lucas, Roger. Boldt Castle, Heart Island. Cheektowaga, N.Y.: Research Review Publications, 1992. Malo, Paul. Boldt Castle: In Search of the Lost Story. Fulton, N.Y.: Laurentian Press, 2001. External links Castles in New York (state) Unfinished castles Thousand Islands Museums in Jefferson County, New York Historic house museums in New York (state) Houses in Jefferson County, New York Houses completed in 1904 Châteauesque architecture in the United States