Lyon's miniature version of the Eiffel Tower was built as a statement in support of French secularism.

This hidden garden boasts amazing views of Lyon.

Hundreds of hidden passageways weave through the old quarters of Lyon.

This Parisian gem is one of the most incredible ethnographic museums in the world.

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

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

In the best of all possible worlds, everyone will get a chance to see this statue in which Voltaire's heart is interred.

A grotto-like lodge decorated with gilded mosaics, rocks and a noisy waterfall was the setting for the most sumptuous pleasure house of 1900s Europe.

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

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

19th century pendulum and a clock restored by a rogue group of guerilla artists.

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

Paris' linguistic guide to the international language of, yes, love.

A tiled, multi-level garden of survival in Lyon.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

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.

Sweden's oldest animated sign is still lighting up the skyline today.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Now a hotel, this former bank was the site of a robbery that spawned a psychological phenomenon.

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.