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

Rebuilt remains of a temple to Roman god Mithras.

The atmospheric road was never meant to be so creepy.

Touching mementoes from those who didn't make it back from World War I still hang in one of New York's oldest bars.

Cryptic messages embedded in the New York City sidewalk.

During the holidays, a vintage subway train whisks New Yorkers back in time.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.

Nondescript elevator doors open to reveal a stunning, surreal world.

Unlock the secrets of the conjuring arts.

Tucked in a nondescript downtown Brooklyn mall is a bar containing a remarkable turn of the century anatomical wax collection last seen in 1920s Berlin.

This beautiful deer park was built so King Charles I and his court could go hunting while escaping a deadly plague outbreak.

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

This former medical factory gives home to cutting edge arts in the shadow of a gas works.

Where Aleister Crowley attempted to seize the Hermetic Order of the Golden Dawn in a mask and a kilt.

Murals of the wild parties once held on the frozen River Thames.

William Blake claimed to have painted this gothic masterpiece after encountering this nightmarish being in a vision.

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

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

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.

This landmark church concealed a crypt packed with bones that was discovered thanks to the London Blitz.

A closed London rail station created to cart away the dead still bears the marks of attempts to make it less morbid.

Tucked inside a South Bank bar is an epic expressionist chronicle of the 20th century.

One of the oldest trees in Britain may have been witness to some of the country's formative moments.

A treasure trove of astronomical, mathematical, and scientific instruments at Cambridge University.