The oldest continuously operating fish market in the United States.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

The United States Capitol's former columns still stand.

This bewitching Babylonian goddess haunts a hallway of the British Museum.

These wire animal sculptures commemorate the exotic inhabitants that once called the Tower of London home.

An architectural oddity hides in plain sight on this iconic London bridge.

A tiny replica of the iconic London landmark hides on the side of the steel structure.

A measuring mishap led to these artificial stone ladies losing their stomachs.

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

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

This long-hidden space above Westminster Abbey now displays the battle gear of the legendary King Henry V.

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

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

A statue marks the exact spot where The Boy Who Never Grows Up made his first literary appearance.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

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

An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

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

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

A public urinal so pretty, it was declared a national monument.

Museum preserving torture methods from the past.