France's national museum of scientific and industrial instruments.

A surrealist timepiece by the artist of melting clocks.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

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

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

Abandoned railway line circling the city of Paris.

Notorious artist squat renovated into legal studios.

France's most famous cemetery, with some of its most curious tombs.

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

A medical facility that has been kept frozen in time.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

An important Mayan religious and trading center dating back to 200 BC.

A massive underwater sinkhole made famous by Jacques Cousteau.

The tallest The Church of Jesus Christ of Latter-day Saints temple in the world soars above the Beltway.

Fiji mermaids, mummified remains, and recreated cryptids are among the morbid oddities at this Maryland museum.

An astounding collection of medical specimens, including bits of President Lincoln.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

Home to items never before seen by the public.

A sharply wedged sundial marks the point at which each day in the United States begins.

This ''hidden'' 19th-century bridge played a simple, yet important role during the Spanish-American War.