The commemorative stone column conceals a secret laboratory.

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

This small collection of rare books was uniquely locked up for safe keeping.

Catacombs turned marketplace.

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

The fences outside some of South London's estates are made from recycled World War II stretchers.

This hidden green space is the city's second largest conservatory.

A tribute to all the green-thumbed workers who tend London’s public parks and gardens.

This one has sailed five times as far as Sir Francis Drake's famous ship.

An incarceration museum on the spot of possibly the oldest prison in England.

The gigantic skull of a long-extinct species that once roamed the forests of England and Ireland.

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

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

A quiet memorial to those who died saving others in the heart of the City of London.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

A tribute to an explorer and naturalist often overlooked by history.

A plaque hangs near the execution place of the Scottish Independence leader famously depicted in "Braveheart."

The bridge is a secret gallery of discarded gum that has been transformed into miniature masterpieces.

London's smallest police station is barely the size of a phone booth.

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

The broken skateboards that became a poignant memorial to a murdered skater.

This South London cemetery holds the remains of more than 15,000 people.

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

A hands-off space for graffiti artists to hone and display their skills.