Emory Minnick has added a photo to the pool:
The ruins of the Hinterhaus Castle originate from the 12th century. The castle dates back to the time of Kuenringers rule when it served as a strategic stronghold. From here they were able to rule the entire Wachau valley.
Source : https://www.flickr.com/photos/emoryminnick/48624916751/in/[email protected]