The Belgian royal family's private depot now stands abandoned and forgotten alongside the tracks.

The tomb of history's greatest potato promoter is surrounded by tubers.

The middle finger of modernity.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

An abandoned Roman salami factory has found new life as an art space home to 200 squatters.

An alchemist's "magic door" stands in the middle of a Roman park.

A random tree outside a Budapest hotel has become a DIY shrine to the late singer.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

This abandoned Belgian fortress is purposefully being left to nature.

Thousands of flowers create enchanting pink tunnels over the city streets.

This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

This Cold War–era fallout shelter was actually a storage facility for the nation's emergency currency.

This Luxembourg cave is covered in cryptic looking marks left by mining activity.

This mansion oasis contains gardens, sculptures, and fountains just off the busy Plaça Kennedy in Sant Gervasi.

A beautiful little museum hidden away in the heart of Barcelona holds a treasure trove of Ancient Egyptian artifacts

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

One of Europe's largest supercomputers is housed inside of a disused chapel.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Week-long block party becomes a competition for the best decorated street.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.