Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

A small horde of mythical creatures lurk almost imperceptibly within the museum's wildlife dioramas.

A Hungarian pharmacy museum with a box full of mummy powder.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Once a mortuary that held the remains of Buffalo Bill, this Denver hotspot is now a death-fixated restaurant.

A technicolor place of worship for Elevationists.

This beautiful system of tunnels built into natural rock serves as a centuries old plumbing system.

At a Bangkok bistro, one pot of beef stew has been cooking non-stop for more than 45 years.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

A spectacular rainbow of stained glass makes the "Pink Mosque" one of the most beautiful in Iran.

Iran's colorful terraces are a rare geological masterpiece.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

These morbid carvings remind churchgoers of the inevitability of death.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

A Roman spa buried deep beneath the City of London.

The last four extravagant street signs of London's historic banking street.

An eccentric 18th century naval officer built a ship's quarterdeck on his roof, the inspiration for Mary Poppins's "Admiral Boom."

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

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

This hidden green space is the city's second largest conservatory.

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

The final resting place to 300 Victorian-era pets hides inside the city park.

Catacombs turned marketplace.

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