Set directly in the side of a large, craggy cliff face, Predjama is certainly one of the most visually arresting castles on Earth. Nestled in the mouth of a cave, its advantageous position made it very hard to attack, and defenders could replenish their supplies through a hidden network of cave passages.

Built and destroyed numerous times over the centuries, Predjama Castle can be found just a short drive away from Slovenia’s capital of Ljubljana. A great time of year to visit is in July, when it hosts a colorful and chaotic medieval festival and jousting competition.