These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

This one has sailed five times as far as Sir Francis Drake's famous ship.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

After nearly 60 years, there's still a bear at Paddington Station looking for help.

Scattered throughout London are ancient remnants of the city's former bounding wall.

London's smallest police station is barely the size of a phone booth.

Hear the quietest sound from across the dome.

A student driver's nightmare.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

The Kirkland Monument remembers a selfless Civil War hero who braved the battlefield to give water to his dying enemies.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

The grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

There’s a hidden military meme engraved on the World War II Memorial.

Decades before the scandal, this staircase on the river was a literal "water gate."

Look closely and you’ll notice that the color changes a third of the way up the tower.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

Once thought to be the fabled Holy Grail, it is now known to be an oil lamp.

Curious crustaceans support an obelisk from ancient Egypt that now stands in modern-day Central Park.

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

This monument to a veteran of the Mexican-American War is one of only two in Manhattan that serve as an actual mausoleum.

During the 19th century, you could pay for violence off a prix fixe menu on this Manhattan street.

Avoid gangster interaction while window-shopping.