A mysterious shape catches the eye in this 16th-century painting.

These marks in Myddelton Passage aren't your run-of-the-mill vandalism, and they weren't made by your typical vandal.

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

This may be the last of London's wooden pavements, which were once a common sight in the city.

It celebrates a very stinky task and salutes London's fatberg-vanquishing team.

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

Following the trail of an old metro line, this scenic path is haunted by a creepy spriggan statue.

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

The secret wartime bunker built on the platforms of an abandoned Tube station.

Drink your espresso at a Victorian-era urinal in this underground-restroom-turned-coffee-bar.

Where condemned pirates met their grisly end at the gallows on the River Thames.

A network of concealed passageways lies within a busy London Underground station.

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

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A kaleidoscopic warehouse-maze of handmade neon signs.

This hidden garden boasts amazing views of Lyon.

The construction of a tram line unveiled hidden remnants of the old medieval city.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

Eduardo Kobra’s breathtaking 32,300-square-foot graffiti wall took over Rio’s Olympic Boulevard.

Out of all the statues of Ho Chi Minh in Vietnam, this one is the tallest and the most impressive.

This historic spot was where America's involvement in the Vietnam War officially came to an end.

Meant to be a lavish presidential home, the palace became a symbol of the fall of South Vietnam.

This French colonial post office is arguably the grandest in all of Southeast Asia.