The largest of London's subterranean rivers and once a mad, bad center of London life.

Louise Bourgeois' 30-foot-tall steel spider sculpture.

A historic arboretum and non-conformist, non-denominational park cemetery.

This legendary stone is of unknown origin, and throughout history has been a literal touchstone for British leaders.

The bears of Bern have been a city highlight for over 500 years.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

Remnants of a Victorian garden feature sitting in public woodland.

These spooky and unusual stone formations create an underworldly landscape.

Surreal riveted sea forts once protected the Kent shores from German attack.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Pitié-Salpêtrière was the dumping grounds for women who received the dreaded diagnosis of "hysterical."

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

One of the oldest masonic museums in Paris.

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

France's national museum of scientific and industrial instruments.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

An antique curios dealer and hybrid taxidermist.

A charming flea market shop dedicated to retrofuturistic apparati.

An ancient monastery, a locked room, and a mysterious book heist.

An intricate and amazing house built by architect Karl Junker.

Museum in a swimming pool where the water still flows.

Colorful and chaotic stacked hotel in North Holland.

A beautifully eclectic mix of architectural styles.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.