The remains of the castle can be visited
Heidenburg Castle
The Heidenburg castle ruin in Stuttgart-Mühlhausen is a local castle, whose origins date back to the 12th century. Today, only a few remnants of the complex remain.
History+
The Heidenburg was presumably built in the 12th century by the Lords of Blankenstein. The Walpurgis Church, which once served as the castle chapel, was first documented in 1275 as the parish church of Mühlhausen. During the Imperial and Cities War of 1312, the complex suffered destruction at the hands of the Esslingers. In 1488, the church nave was extended, and in 1567, the church was converted to the Protestant denomination. Under the patronage of the Barons of Palm, the church tower received an octagonal addition in 1812.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Ruine_der_Walpurgiskirche_Stuttgart-M%C3%BChlhausen.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: 48.8442, 9.2309