A unique collection of gilded age mechanical pianos.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

Amsterdam's Red Light District leaves little to the imagination.

This bronze statue of Martin Luther King was placed in the park without permission.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

This vast collection of smoking pipes from across the world spans centuries.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

The largest collection of handbags in the world, the oldest of which were used to carry Bibles, primarily by men.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

Paris' fabled purveyor of exotic taxidermy and natural history curios.

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

Notorious artist squat renovated into legal studios.

A bronze statue of the famed Prussian naturalist commemorates the year he spent in Mexico.

The ruins of the "place of the cloud snake" sit in the middle of an urban environment.

These subterranean models show Mexico City's central square during three different eras.

Its exhibits are dedicated to educating the public about state terrorism in Mexico.

Inside a busy metro station, an impressive mural depicts the prehispanic city of Tenochtitlán.

This foreboding building was the headquarters of the terrifying Spanish Inquisition in Mexico.

A jaw-dropping "megalibrary" that turns book-browsing into a geometric adventure.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The historic Masonic Lodge in which the first-ever female Mason was initiated.

This structure atop a craggy cliff in one of the most beautiful parks in Paris boasts an unbeatable view.

A magical, macabre wax museum, beloved by locals, uses real artifacts to depict an assassination from the French Revolution.