The largest and best-preserved Roman amphitheater in Africa was designed to seat 35,000 people.

This grand hydraulic installation has provided water for townspeople since the Middle Ages.

Founded in 670, this ancient mosque is an architectural time portal.

Catacombs turned marketplace.

This tribute to the fictional detective stands at the famous literary character's address.

A plaque marks the underground site of one of London's "lost rivers."

This London marker celebrates the spot where the world-famous English band was founded.

The John Snow Memorial marks the epicenter of London's 1854 cholera epidemic.

This ancient oak plays host to carvings of magical elves, gnomes, witches, and other creatures prominent in local folklore.

Two tombstones associated with the much-beloved children's story.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

A commemorative plaque at the door pays tribute to an "American Patriot" known for his betrayal.

Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

A building claimed to be London’s smallest house has an obscure history.

The final resting place to 300 Victorian-era pets hides inside the city park.

You'd never know the houses at 23-24 Leinster Gardens were fakes—until you see the train tracks on the other side.

The bust of a 15th-century Albanian leader in the middle of London.

Legend says these colorful, invasive residents are the descendants of birds released by Jimi Hendrix.

Latvia’s first skyscraper, nicknamed ‘Stalin’s birthday cake.’

A unique underground structure dating back to the 1st century BC.

This ancient theater was once the home of fierce gladiatorial battles.

The lost Latin words were reconstructed using the holes from the nails that once pinned them in place.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.