Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

Eighty million natural history specimens call this gargantuan museum home.

The longest hedge maze in the world.

A special shop catering to the needs of things that go bump in the night, and also helps kids become writers.

The curios of pharmacist and collector Henry Wellcome.

A vast overgrown cemetery, once known as one of London's "Magnificent Seven."

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

One part local history, 99 parts gruesome haunted house.

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

The only university zoological museum in London houses extinct animals, bizarre natural history specimens, and a Micrarium of microscopic creatures.

An unusual round church in London with a Templar past.

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

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

A tongue-in-cheek arcade where the games are based on everyday life.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

The world's largest collection of witchcraft regalia.

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

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

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

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

The sign at the garden gate reads: "These Plants Can Kill."

Kings Cross Station pays tribute to its role in Britain's best-selling book series.