The Fortress can be visited
Heldrungen Fortness

Heldrungen Fortress, a complex with double moats and prominent bastions, is situated in Thuringia. It combines the history of a medieval castle with the defensive strength of an early modern fortress.
History+
The origins of Heldrungen Fortress date back to the 13th century, when a castle was built on this site. Around 1190, a stone Romanesque complex was erected, owned by the Lords of Heldrungen. Later, the castle passed to the Counts of Hohnstein, who sold it to Count Ernst II of Mansfeld in 1479. From 1501, he had the complex renovated and expanded into a residence. Between 1512 and 1518, the four-winged Renaissance castle was built. After 1519, the castle was converted into a fortress with two defensive rings and twelve roundels, considered impregnable. During the German Peasants' War in 1525, it served as a refuge for the nobility and was the place where the captured peasant leader Thomas Müntzer was held until his execution.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 51.2989, 11.2189