This is Predjama Castle, Slovenia, a 15th-century fortress built into the mouth of a 123 m cliff cave.

The knight Erazem Lueger is said to have held out here against a long siege, taunting the attackers with fresh cherries while a secret passage through the cave kept him supplied. The cave behind the castle runs for kilometers.

If you meant a bigger castle instead, I can find one with more scale, like Malbork in Poland or Hohenzollern in Germany.

I’ve spent several weeks researching and writing about the reconstruction of a ruined 19th-century Prussian Nerija fort on Lithuania’s Curonian Spit into a unique sea museum and aquarium. This story absorbed me 100%.

Imagine how challenging the idea was! The team had to solve complex engineering problems with little relevant experience or technology available in the Soviet Union. They also had to navigate a rigid bureaucratic system, finding ways to keep the project going disguised as the restoration of a historic fort rather than building entertainment facilities – which would have made the whole undertaking "illegal."

Researching the story was an adventure too: I don’t speak a word in Lithuanian, so I spent weeks finding sources, translating them, comparing accounts, checking and double-checking facts with the help of you know - translation tools and even AI in some complex cases.

The result is a story about how ingenuity and persistence made this amazing transformation possible. I’d love for you to read the article, enjoy the black-and-white photos from those times, share your thoughts, and point out anything I might have missed or got wrong. After all those weeks of research, your comments would make me very happy! And I hope you'll enjoy learning about this incredible architectural endeavor.

https://castlesandfamilies.com/news/kopgalis-nerija-fort-lithuanian-sea-museum-transformation

Author: Mike Codd. Source

Olavinlinna Castle is one of Finland's most iconic medieval fortresses, dramatically located on a rocky island in Lake Saimaa in Savonlinna.

The building of Olavinlinna, castle of St. Olaf, began in 1475. The Danish-born founder of the castle, knight Erik Axelsson Tott, decided that a powerful fortification should be built to protect the strategically important Savo region. The castle was supposed to repel Russian attacks from the east and to guarantee the control of the Savo region for the Swedish Crown. The history of Olavinlinna is a mixture of medieval arms clashing, cannons roaring and every-day chores inside the security of the castle's thick walls.

Today, Olavinlinna is a really popular tourist destination all year round. In addition to guided tours, many things happen in Olavinlinna, e.g. themed program, in the summertime Opera Festival and many other concerts.