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

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Legions of Roman soldiers bathed in this ancient spa complex under a Budapest transit station.

This quaint Hungarian railway system is operated exclusively by children between the ages of 10 and 14.

The abandoned "Red Star Train Graveyard" is the final rusting place for precious artifacts of train history.

This hanging crocodile is thought to be the "dragon" that once plagued a Czech city.

A cheeky architectural easter egg.

A peculiar clock commemorates a historic victory won by ringing the noonday bell an hour early.

A former top secret nuclear fallout shelter now operates like a hotel stuck in the Cold War.

This museum in a Paris apartment gives a unique look at the iconic French singer's life.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

The Cimetière des Chiens et Autres Animaux Domestiques is one of the oldest pet cemeteries in the world.

A subterranean shelter remains intact under a busy Paris railway station.

This surreal statue brings a famous French novel about a supernatural cad to arresting life.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

A kaleidoscopic warehouse-maze of handmade neon signs.

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

A open air theatre built on a cliff by an eccentric British woman.

400-year-old garden, restored to beauty.

The largest greenhouse in the world is home to over one million types of plants.

The biggest and deepest Cold War bunker open to the public can be found in southeast England.

Eclectic final resting place of the controversial explorer.

Abstract dinosaur models in London.

The remains of Crystal Palace Great Exhibition of 1851.