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

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

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

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

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

A relic of Victorian grandeur hides beneath a busy South London road.

The first tunnel to be dug beneath a river, repurposed as an art and museum space.

A Roman spa buried deep beneath the City of London.

This artist's home turned gallery/museum preserves the creator's love of "Eastern" influences.

The lab where the scientist made his groundbreaking discoveries is preserved on the basement floor of the Faraday Museum.

This museum tucked below a charming cafe gives a brief snapshot of photographic history.

Claiming to be the oldest hat store in the world, this historic haberdashery had a hand (and a head) in the creation of the Bowler.

The pioneer of psychoanalysis spent the final year of his life here, still seeing patients on that famous couch.

The London pub overlooks where the Mayflower was moored before setting sail for the New World.

19th-century scientists would make the pilgrimage here to verify the precision of their measuring sticks.

A mysterious pair of mice eating a piece of cheese is London's smallest public sculpture.

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

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

A statue marks the exact spot where The Boy Who Never Grows Up made his first literary appearance.

English antique dealers with a taste for the unusual.

A toy store with a century-long history preserves the craftsmanship of playthings of the past.

Repository for more than 22 million pickled specimens.

The largest of London's subterranean rivers and once a mad, bad center of London life.

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