Enormous, fluffy dogs frolic around this museum dedicated to a legendary Saint Bernard.

A subterranean shelter remains intact under a busy Paris railway station.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

Abandoned railway line circling the city of Paris.

A once-fairy tale mansion now stands in a state of disrepair.

This obscure walkway links Edinburgh’s Old Town with one of the city's prime vantage points.

Long abandoned underground complex to keep royals safe from a nuclear war that never came.

An American ghost town hides along a side street in Scotland's capital.

This series of Scottish caves has no clear purpose other than baffling historians.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

This former train tunnel is filled with lines from a poem crafted by Robert Louis Stevenson.

One of the few places to grab a beer in Fez is a former British consulate.

Crumbling necropolis set high above Fez.

Along the most northwestern point in Africa is an ancient cave surrounded by legends.

A relic of the Cold War tucked away in the forested hills above Bratislava.

A line of disused military bunkers built to defend against Nazi invasion lies hidden on the outskirts of the city.

A unique hotel for the artistic soul.

The house that took a plunge into the facade of a museum.

The housing complex served as an anti-fascist fortress during the Austrian Civil War.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

Apartment complexes built into huge repurposed natural gas tanks.

Located right outside of Vienna, visitors can take in expansive views of an ethereal forest.

A spherical "micro-nation" in the heart of Vienna.