A former ironworks that was the first UNESCO industrial site.

Each spring, a dreamlike carpet of bluebells overtakes the forest floor.

This private museum is packed with 20th-century traffic and technology artifacts.

Centuries of warfare, tragedy, executions, and poetry come together in this 13th-century fortress.

A tiny chapel clings to a precipice above Germany’s gemstone capital.

Germany's longest suspension rope bridge.

The private train station King Leopold II built for the Belgian royal family now lies abandoned.

A whimsical bridge uses saxophones to pay tribute to two great men and the European Union.

This professional clown's home is an outsider art wonderland.

Built to test magnetically levitated elevators, the tower also boasts Germany's highest visitor platform.

This old wooden funicular railway leads to a cemetery in the forest.

Remnants of a cone-shaped Nazi bomb shelter.

This outdoor library provides around-the-clock access to around 7,000 books.

The Cimetière des Chiens et Autres Animaux Domestiques is one of the oldest pet cemeteries in the world.

Indents in the pavement are all that remain from a grisly death machine in Paris.

Ghosts of France's colonial past.

The man who introduced reinforced concrete to the world demonstrated its genius by using it to build his own house.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

Despite being considered a thoroughly American sport, basketball's oldest surviving playing field is found in the basement of a Paris YMCA.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

The sunken structure looks like the victim of a catastrophic flood.

Abbey built on the ruins of Roman catacombs.