You can visit a castle in Slovenia that was built into the mouth of a cave and features hidden passageways

• The Predjama Castle in Slovenia, which has been listed as the "Largest Cave Castle," is a stunning structure perched on a 400-meter cliff. 
• The castle is open to the public year-round. Visitors can also buy tickets to explore the Postojna Cave below. 
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The only thing more fairytale-like than a castle is a castle perched on a 400-meter cliff that's built around the entrance of a natural cave. Oh, and did we mention there's a network of secret passageways? The Predjama Castle in Slovenia has all that and more — and it's open to the public year-round.

Originally dating back to the 13th century, the medieval castle is listed in the Guinness World Records as the "Largest Cave Castle." The structure is not only built into the side of a cave, but also sits on top of the second-longest cave in Slovenia, which spans four floors.

The castle was used as a fortress for many noblemen over the years, which is why the secret passageway was so crucial. According to My Modern Met, the knight Erasmus of Lug (Erazem in Slovenian) was the lord of the castle in the 15th century. He was a well-known robber who was forced to flee when he killed the commander of the imperial army. The castle became his refuge, and from there, he used the hidden passageways to get supplies and continue his robberies.

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Today, Predjama Castle is open year-round to visitors who can also buy combo tickets to see the great Postojna Cave below. For the latter, visitors can access over three miles of chambers, passageways, and cave formations beneath the earth.

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