A Roman spa buried deep beneath the City of London.

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

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.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

Rebuilt remains of a temple to Roman god Mithras.

What might be the oldest living tree in London has survived fires, bombings, and estate agents.

A commemorative plaque at the door pays tribute to an "American Patriot" known for his betrayal.

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

A portly statue of a golden boy commemorates an unusual cause of the Great Fire of London: the sin of gluttony.

Remnants of cells from the most notorious London prison may lie in the basement of a rare Victorian Gin Palace.

Originally built for London’s cab drivers, this bright green hut now serves anyone a hot drink or meal.

A lasting remnant of The Blitz.

This overlooked street light once served as a KGB dead letter box.

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

One of the few remaining examples of 19th-century London’s attempt to clean up its reputation.

A collection of comics, graphic novels, animation and caricatures devoted to exploring this often overlooked art form.

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

A naturally mummified 2,000-year-old man.

On October 17, 1814, a 15-ft. wave of beer ran rampant through the streets of London.

Victorian-era Londoners really wanted to believe this 17th-century cistern was actually an ancient artifact.

This Underground station has been a popular filming location for decades, even before it closed.

The John Snow Memorial marks the epicenter of London's 1854 cholera epidemic.

This luxury shopping lane has been protected by its own tiny police force for over a century.