The Archway Building stands at the entrance to the palace area. It is thought to be built by Franz Anton Bagnato, the son of the palace’s architect. The date 1764 and the coat of arms of the provincial commander Count Königsegg support this assumption. The classic extension dates back to the 19th century. There was once a moat in front of the building. Today, the building houses part of the Mainau administration and also the Mainau Service Centre where brochures about Mainau and the Lake Constance region are available.