Castle Aggstein-one of the sights of the cruise

Seemingly precariously perched atop this mountain, Castle Aggstein has a perfect view of the Danube.
Originally built to to protect merchants travelling through the Danube Valley, it was eventually taken over by a robber Baron who delighted in forcing his "guests" to leap off to plunge into the depths below.

Apparently it's quite a nice walk up and it's even been a little restored. Something else to put on the to-do list.