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

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

The Metropolitan Police refurbished the blue box (perhaps not coincidentally) the same year "Doctor Who" returned to TV screens.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

This abandoned Slovenian military barracks has become a punky-political art squat.

The shell of a medieval fortress offers commanding views of the area it once protected.

An artistic tribute to the famous singer, just around the corner from where he was born.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

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

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

Double spiral staircases are not unheard of, but they are very rare.