The remains of the Castle can be visited
Zähringen Castle

The Zähringen Castle Ruin, the ancestral seat of the Zähringen noble family, is located on an outcrop of the Roßkopf above the Freiburg district of Zähringen.
History+
An Alemannic hilltop settlement existed on the castle hill from the 3rd to the 5th century. The first confirmed mention of Zähringen Castle dates back to 1128. Berthold II relocated his seat in 1091 and began constructing Freiburg Castle, as its location was strategically more favorable. After the extinction of the Zähringen family in 1218, the castle became an imperial fief under Emperor Frederick II.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Burg_Z%C3%A4hringen_%28Freiburg_im_Breisgau%29_02.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: 48.0253, 7.8842