This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

One of the world's largest collections of pathological specimens.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

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

This 1920s Dutch barge is now a floating bookstore.

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

The remains of Crystal Palace Great Exhibition of 1851.

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

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

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

The anatomical-pathological collection of a man who changed surgery.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

A student driver's nightmare.

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

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

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

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

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

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

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

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

A kaleidoscopic warehouse-maze of handmade neon signs.