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

Eighty million natural history specimens call this gargantuan museum home.

A student driver's nightmare.

One part local history, 99 parts gruesome haunted house.

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

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

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

Banksy gives themself artistic license with this piece of London street art.

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

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

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

This ancient altar emerges from the thick forests to reveal the mysteries of Etruscan sacrificial rituals.

The abandoned ruins of a failed resort hide on this verdant, picture-perfect island.

The top of society once luxuriated in this world-class hotel, which continues to impress, even in ruin.

A madman's personal garden filled with 1,000 sculpted heads.

Crumbling ruins of the thermal baths that once attracted royals and aristocrats from throughout Europe.

Geometry and mystery come together in an epic show of octagonal masonry.

This seaside Italian village doesn't just look Escher-esque, it actually inspired the mind-bending artist.

One of the world's oldest working clocks is curiously missing the Zodiac sign of Libra.

Beautiful views and Roman-style statues on the Italian coast.

A small window on Via Piella offers a lovely and rare peek at Bologna's lost canals.

A fairytale-like medieval church perched atop a rocky cliff on Italy's "Coast of the Gods."