Graffiti from the 16th and 17th centuries cover the walls of this part of the Tower of London.

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

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

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

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

The 2,000-year-old beam is tucked within the pedestrian entrance to the old London Bridge.

The Great Fire of London and the regulation of one-way streets both started in this alley.

The commemorative stone column conceals a secret laboratory.

These Victorian era devil sculptures were designed to spite a local vicar.

The site of London's first coffee house has been serving refreshments of one kind or another for 360 years.

The last four extravagant street signs of London's historic banking street.

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

London's amazing modernist public square that never was.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

This 1920s Dutch barge is now a floating bookstore.

Catacombs turned marketplace.

This sculpture encompasses the emotion of rail travel.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

Portugal's National Pantheon has a history of curses, collapses and financial problems.

This unique architectural wonder is also tied to one of the 20th-century's most renowned writers.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This once-forgotten oasis in the middle of Lisbon was first created over a century ago quite by accident.

One man's remarkable private collection of art from around the world.