This historic Amsterdam bar used to accept sailor's monkeys as payment.

A floating cat sanctuary on an Amsterdam canal.

Cat art as far as the eye can see.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

2300-year-old Roman road connecting the empire.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

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

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

A sweet symbol marks the place where torturous executions were once carried out.

A 18th century graveyard and its astonishing cortege of macabre iconography.

360° views of the city plus five floors of optical illusions and hands-on science.

The gloomy ruins that inspired Bram Stoker to bring Dracula to life.

The fake World Cup prize was secretly created after the first one was stolen in 1966.

Manchester salvaged this sculpture of the adopted Mancunian when it was no longer wanted in Ukraine.

This 19th-century fountain's namesake animal isn't what you think it is.

Giant topiary dog once played a role in a terrorist bomb plot.

Once a dumping spot, now a park with a kayak launch.

Ride the subways of yesteryear.

The one-stop shop for all of your superhero (or evil arch-nemesis) needs.

These historic buildings once housed the headquarters of one of the most infamous gangs of New York.

The artist and New York City icon lived, worked and died in this converted carriage house owned by another iconic artist, Andy Warhol.