Diessenhofen's Unterhof Castle was first mentioned in 1185, although it is not certain who built the castle. It was the seat of the Trustees of Diessenhofen. In 1264 the castle became the property of Rudolf von Habsburg, who took the stewards into his service. In 1460, the stewards' administrative mandate ended when the city was taken over by the Confederates. The castle finally came into the possession of the Lords of Randegg in 1474, before it belonged to the Knights of Schellenberg in the years 1627-1725. Finally, the Junker von Greuth sold the castle to the city in 1725.
Diessenhofen set up apartments and even an eye clinic, although an insurance company bought the castle in 1990 and completely renovated it by 2002. A seminar hotel was set up.
Today the castle belongs to a Schaffhausen real estate company. The old part of the castle is used as a restaurant, the rest of the castle houses apartments again.