This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

England's most famous front door has an accidental doppelganger.

The commemorative stone column conceals a secret laboratory.

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

More than a million titles fill the labyrinthine shelves of this prestigious private library.

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

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

A musical composition 1000 years in length plays at the Trinity Buoy Wharf in London.

This beautiful Victorian ironwork masterpiece was built to keep London from smelling like poop.

A clock designed to run with perfect accuracy for 10,000 years.

Hidden beneath the streets of London is a secret subway that only carried mail.

A collection of machines designed to break things for science.

A network of bells in the pubs and restaurants around Westminster alerts politicians when it's time to cast their votes.

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

This unique bridge curls up like a caterpillar to let boats pass and then unfurls again to span a small canal.

The Tudor-style cottage in the middle of the square is not quite what it seems.

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

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

The remains of the great moral philosopher reside in a university in London.

Ship-sized kinetic sculptural fantasy.

Public access to clean drinking water was an instant hit among the masses.

Charles Babbage's proto-computer, painstakingly brought to life.

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

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