Secret refuge and museum of the Duke of Florence.

Art and armour fill every inch of this rich kid's Italian villa.

A stunning bridge that appears as if it's lunging to the shore, and has a legend of a devilish architect.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

An icy lake tucked among jaw-dropping alpine panoramas.

Renaissance villa and gardens complete with a tormented colossus.

The remains of the last Bosnian fortress to fall to the Ottomans are still standing.

A factory director designed what was the world's longest suspension footbridge in 1923 so his employees could get to work safely.

This cluster of little wooden huts once ground local farmers’ wheat into flour during the days of the Austro-Hungarian Empire.

Eco-village hidden in the foothills of the Alps that created a massive system of psychedelic underground temples.

Over 3km of caverns and caves at the Switzerland-France border contain the largest underground river in Central Europe.

A formerly opulent Italian village is now a crumbling ghost town that no one really knows what to do with.

This natural gas vent certainly earns its name as the smallest volcano in Italy.

Abbey built on the ruins of Roman catacombs.

Swiss vineyards in a UNESCO heritage site.

A gorgeous medieval library where the books are kept in chains.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

A towering baroque basilica jutting out of the French countryside.

A once-magnificent collegiate church is falling into ruin.

A marble Lucifer hides behind the pulpit of this Gothic cathedral.

This abandoned Belgian fortress is purposefully being left to nature.

Religious perseverance and cultural coexistence manifest in an architectural gem that multiple wars couldn't topple.

Italy's curious field of mud volcanoes is named for being both gross AND salty.

This abandoned Croatian stronghold never saw a great deal of conflict but it is still a beloved relic nonetheless.