The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A submerged archeological park still holds the wonders of a Roman Sodom.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

A 16th-century horror show built in a lovely Italian garden.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

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

Commonly acknowledged as the only public monument to the Devil himself.

A lush indoor jungle fills this bustling Madrid transportation hub.

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

The little church's beautifully frescoed ceiling has earned it the nickname “the Sistine Chapel of Madrid.”

The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

The great Danube river starts here.

This natural hill rose another 130 feet from the debris and rubble added after World War II.

This lurid German fountain plots the sad course of marriage from dating to death.

This walkway is so narrow it needs its own light to stop pedestrian traffic jams.

The world’s narrowest house makes for an awkward, four-foot-wide living space.

The unsettling remnants of a torn down movie set lies nearby the ruined location of the actual Płaszów Labor Camp.

While the U.S. and Soviet Union were engaged in a space race, Poland built a UFO on the ground.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

This series of Baroque passageways in Vienna's cultural center mix old architecture with modern art.

The solemn exterior conceals an opulent interior of this 17th century church.

A neo-Gothic church built to thank God for saving the Emperor of Austria from an assassination.