Guided tours of this National Monument take place at the top of the hour daily. The pentagonal building was built by Pieter Dombaer in the shape of a five-pointed star, following a construction system based on French military engineer Vauban. The five bastions carry the titles of the Prince of Oranje: Leerdam; Oranje; Buren; Catzenellenbogen; and Nassau. The bastions housed the military, provided storerooms, prisoners' cells and torture chambers. Come and see the formal changing of the guard at noon on weekdays.