Abandoned Nazi train station turned underground astroparticle laboratory.

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

This secluded walkway overlooks a magnificently wild London green space.

An ancient Egyptian temple in the middle of Madrid, Spain.

The unfinished final resting place of some of Spain's most prominent politicians.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

A lush indoor jungle fills this bustling Madrid transportation hub.

One of Madrid's oldest trees, with a long and colorful history, resides in El Retiro Park.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

A whimsical brother of the nearby Fallen Angel statue takes the falling part quite literally.

An automaton perched above an classic clock and watch store

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

For decades, Puerta del Sol has been illuminated by a giant, guitar-wielding bottle of sherry.

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.

This massive blockhead sculpture hides an entire library.

An Orthodox church built by the Royal Family for the Russian community exiled to the French Riviera.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

This iconic high-rise residential block was one of the last to be built in the Brutalist style.

A magnificent, glittering building tucked into a tiny Bulgarian mountain town.

An abandoned saucer-shaped monument in the Bulgarian mountains.

Eastern Bloc nostalgia, anybody?

An exercise in radical design and social living that became the epicenter of Soviet spy networks in London.

A stunning cemetery famous for its extraordinarily delicate & lifelike mourning sculptures.