This little-known relic crypt holds stolen parts of a Roman Empress.

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

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

Statue of death tucked in the University of Medicine courtyard.

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

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

This museum houses an imposing skeleton army comprised of creatures great and small.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

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

A haunting collection of the vanished and disappearing natural world.

One of the oldest medical collections in Europe focusing on rare surgical instruments.

The oldest stone house in Paris was built by its most famous alchemist.

Notorious artist squat renovated into legal studios.

This massive library holds what was once the largest book collection in the world.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A decommissioned submarine base makes a great space for graffiti art.

A series of concentric circles represented a bold new experiment in socialist urban planning, and it notoriously difficult to get around.

One of the oldest lighthouses in the world has been in continuous use since it was first built in 1531.

This abandoned office building is a lasting example of Soviet-era architecture.

This former medieval prison now unlocks Estonia’s rich photographic history.

This striking memorial is one of Estonia’s most controversial Soviet leftovers.

This old Estonian mine has been kept like a sprawling time capsule of the local shale industry.

The oldest church in the Estonian capital is home to over 100 fantastical cemetery coats-of-arms.

Abandoned Soviet base once stocked with short and medium range missiles pointed at western Europe.