The remains of the Castle can be visited
Dürnstein (Old) Castle

The Dürnstein Castle Ruin is one of Austria's most renowned historical structures. Its fame stems, among other things, from the imprisonment of an English king within its walls.
History+
The construction of Dürnstein Castle took place around the mid-12th century by the Kuenringer family. Hadmar I, a grandson of the Kuenringer patriarch Azzo von Gobatsburg, who had acquired the surrounding land from Tegernsee Abbey, was the builder. A distinctive feature is the castle's connection to the town of Dürnstein via a continuous defensive wall. The site gained notoriety when King Richard the Lionheart of England was held captive here between December 1192 and March 1193, at the instigation of Duke Leopold V under Hadmar II, before being handed over to Emperor Henry VI. A castle chapel, dedicated to John the Evangelist, was first mentioned in 1306. In 1588, Streun von Schwarzenau had the castle converted into a fortress.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Maciek Wegrzyn
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: 48.3978, 15.5219