Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

This secret garden has bloomed into London's most unique hub of urban creativity.

This small museum in a former church crypt contains artifacts of the Elephant Man, Jack the Ripper and Florence Nightingale.

Preserved behind glass, the ruins of a medieval building used to store human remains.

This unassuming building produced some of the world's most famous bells.

The last remaining example of the boatmen's perches that once dotted the south bank of the Thames.

The ground on which Shakespeare’s initial playhouse once stood.

At Bank station, the tunneling shield that built the original Waterloo & City line tunnel is hiding in plain sight

Metal horses galloping through a London fountain provide a link to the city's past.

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

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

This pump on the bad side of Victorian London betrayed a horrifying revelation about the water supply.

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

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

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

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

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

Richard III supposedly disposed of his nephews' bodies here in an effort to seal his claim to the throne.

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

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

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