The Predjama Castle.... such a beautiful place. It is literally a castle built inside (and outside) of a cave ! It was built as a tiny castle to protect its inhabitants from a barbaric middle age world, and soon was upgraded, century after century, in what is now this huge building. It became a museum that shows the life inside as it was back in the days. We can even enter the troglodyte part, that is completely inside the cave. You could walk through it for 14 kilometers!