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

This coffee shop lies hidden beneath a historic church.

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

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

Designed by the architect who also had a hand in crafting the Westminster Abbey and Bristol Cathedral.

This 19th-century pub features stained-glass windows celebrating Victorian-era "champions."

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

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

Classic game cookery takes center stage at what's widely considered London's oldest restaurant.

The Tudor-style cottage in the middle of the square is not quite what it seems.

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

The Art Deco artwork depicts gilded carriers of deadly illnesses.

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

A naturally mummified 2,000-year-old man.

The site of the "Bone Wars" between two rival paleontologists during the dinosaur rush of the 19th century.

This Colorado hiking trail provides a small gold mine of abandoned gold mines.

The largest source of fossilized insects anywhere.

The show pony of cave systems, Fantastic Caverns manages to live up to its name.

400 million-year old limestone caverns nestled in the Ozarks served as shelter and a hideout for cultures throughout North American history.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

Erosion and time have created a naturally-formed water park.

The world's largest man-made underground caverns offer unparalleled underwater wonders.

The history of the treatment of mental illness, illustrated in all its gory detail, and housed in an asylum.

Once an ambitious nature spa, these forest ruins now provide a serene monument to failure.