This five-star hotel was originally a swanky parking garage.

It is still illegal to "quarrel" at this unlikely urban oasis built on top of an electrical substation.

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

This once-controversial and slightly confusing statue of Achilles was built out of captured cannons.

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.

This striking statue brings a scene from the African savannah into central London.

Tucked away behind the mansions of Mayfair, this picturesque garden is a hidden London treasure with a spooky past.

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

Infamous and now demolished panopticon prison built by its former inhabitants.

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

A small museum displays some of the artifacts discovered during a subway station renovation.

Sometimes called the Banksy of Madrid, Muelle was a pioneer of street art in the Spanish city.

Part of the medieval watchtower is displayed in an otherwise ordinary parking garage.

This small museum tucked within a subway station holds pieces from Madrid's past.

An old, deep well, connected with a miraculous, divine rescue and the patron saint of Madrid.

Remains of the lost church hide beneath this Spanish Parliament building.

A towering monument in Spain has proven to be more labor-intensive than initially planned.

A magnificent, long-abandoned castle built in the wake of the reconquest of Spain.

The little church's beautifully frescoed ceiling has earned it the nickname “the Sistine Chapel of Madrid.”

This amazing abuela became a diehard metal fan late in life and an icon of Madrid's '80s rock scene.

Dedicated to a young woman who broke gender barriers at the University of Madrid.

The remains of a convent turned military barrack in the heart of Madrid.

A 12th century church completely covered in shells.

Seaside ruins of a settlement that date back to the first century B.C.