Hohenasperg
Ludwigsburg District, Germany · built 1535
Hohenasperg, located in the federal state of Baden-Württemberg near Stuttgart, Germany, of which it is administratively part, is an ancient fortress and prison overlooking the town of Asperg. It was an important Celtic oppidum, and a number of very important "princely" burials are close by, in particular the Hochdorf Chieftain's Grave.
Prison data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).