Chelsea's soldiers were given strict orders when crossing this historic bridge.

Only a few pieces remain of the structure that carried people and goods across the Thames for some 600 years.

The sculpture of the deceased cockatoo flops atop its personal plinth.

Visit the grave of a famous feminist author and the mother of Mary Shelley.

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

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

The barrel-made lookout from Shackleton's final ship is tucked away in the crypt of one of London's oldest churches.

A memorial for public executions that dates back to the 14th century.

The Brutalist building harbors an unusual inverted dome that swoops down over its central sacred room.

A wonderfully preserved example of London's 1960s-style high-density, low-rise public housing.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

This 19th-century pub features stained-glass windows celebrating Victorian-era "champions."

Hidden beneath the streets of London is a secret subway that only carried mail.

A faded reminder of what was once a common sight in London during the Blitz.

A lasting remnant of The Blitz.

One of Madrid's oldest trees, with a long and colorful history, resides in El Retiro Park.

This piece of early engineering is rather unknown despite its location in the heart of Madrid.

One of the best examples of the modernist movement in Madrid.

This lucky bronze frog was gifted to Madrid by a casino.

This royal shrine and cemetery is hidden amidst modern public housing.

A venerated grave atop an ancient royal hill, often attributed to the last king of Singapura.

A statue that would be at home in Rome can instead be found in the heart of Norway's oldest city.

This one-of-its-kind shipyard brings the 12th-century Viking Age back to life.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.