The remains of the Castle can be visited
Aach Castle

The Aach Castle Ruin, also known as Alter Turm (Old Tower), is a hilltop castle in the Hegau region. It is one of the oldest of its kind in the region.
History+
The origins of the Aach Castle Ruin date back to the early 11th century, specifically the first quarter of that century. This was confirmed by a C14 dating of a charcoal piece from the masonry. A noble family named Odalricus de Ake, mentioned in a document around 1100, is considered the probable builder of the tower. From 1158 onwards, the castle came into the possession of the Prince-Bishopric of Constance.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Turm_Aach_2.jpg
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: 47.8483, 8.8589