The Castle can be visited
Mainau Castle

On Mainau Island in Lake Constance stands Mainau Castle, a Baroque edifice. It was built on the foundations of a former castle and still serves as the residence of the comital family.
History+
The construction of Mainau Castle began in 1739. It was erected on the site of a castle demolished in the 18th century. The plans for the three-winged Baroque castle were drawn up by Johann Caspar Bagnato, who also supervised its construction. After a seven-year building period, the castle was completed. It was designed around a courtyard of honor and also included a side terrace garden. A detail on the central risalit is the large coat of arms of the Teutonic Order.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Norbert Kaiser
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 47.7050, 9.2001