The signs of a long buried road can still be found hidden beneath a London sewer grate.

The final resting place to 300 Victorian-era pets hides inside the city park.

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

A historic London pub with prison cells in the cellar and a "spy room" on the second floor.

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

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

Remnants of a Victorian garden feature sitting in public woodland.

Catacombs turned marketplace.

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

Rebuilt remains of a temple to Roman god Mithras.

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

This 1920s Dutch barge is now a floating bookstore.

A student driver's nightmare.

One part local history, 99 parts gruesome haunted house.

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

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

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

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.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

In the middle of a Vienna square, Roman ruins dating back some 2,000 years are on display.

This museum is dedicated to the little known ancient Roman history of Vienna.

The first modernist church in Europe.

This grand manse has been transformed into a museum devoted to one of the founders of Fantastic Realism.