This Gothic gem, a replica of a German castle, was (partly) built by tycoon hotelier George C Boldt in the late 19th century. In 1904, however, midway through construction, Boldt's wife died suddenly, and the project was abandoned. Since 1977 the Thousand Islands Bridge Authority has spent millions restoring the place to something of its planned grandeur.

One floor of the main castle building has been finished the way Boldt intended, with other buildings on the island secured and the gardens brought back to life. Access to the castle is by boat (additional fee) from Clayton or Alexandria Bay.