A marvel of Byzantine engineering under the streets of Istanbul.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

An ancient ossuary in Rouen.

This medieval tower is all that remains of the castle where Joan of Arc was held before being burned at the stake.

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

Lyon's "Wall of the Silk Weavers" is one of the largest murals in Europe.

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

This centuries-old pub boasts a collection of more than 4,500 snippets of neckties from around the world.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

Longest canal tunnel in the world, abandoned in the 1960s.

This frog-themed restaurant was frequented by Picasso, Saint-Exupéry, and more.

Hundreds of secret cabinets built into the walls of legendary poisoner's private work room.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

Budapest's Communist-era statues, banished to the suburbs.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

Mexico City's largest market contains a Willy Wonka-esque wonderland.

Iconic Los Angeles residence famous for its 19 statues of Michelangelo's David.

This centerpiece of the Hollywood & Highland shopping center is a recreation of a long-lost movie set.

The decor of this Hollywood movie palace just barely predated the opening of King Tut's tomb.

The blinking light atop the iconic landmark has been sending secret messages for decades.

The space-age building is home to one of the few remaining rotating restaurants in America, and the only one that inspired a 1980s sitcom.

Once strictly off-limits, this lower level housing curious and priceless vehicles of the Petersen Automotive Museum is now open to the public.

Dozens of feral felines rule a segment of Hollywood's only graveyard.