Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

Faceless white figures loom over the city from the rooftop.

A man-made island in scenic San Francisco Bay.

I Street Bridge is the heaviest swinging center bridge in the United States.

Puzzling...this tree looks like an assemblage of dismembered monkey limbs.

Finale of "William Tell Overture" can be heard as drivers pass over grooves in the road.

California's oldest wind harp represents a historic piece of America's Danish history.

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

This giant shopping mall still holds signs of its automotive past.

A house built from trash known as the poor man's Hearst Castle.

A remote crossroads honoring a fallen talent.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

A minotaur, a labyrinth, and a dubious restoration pull in visitors from around the world.

This famous archeological mystery may be an ancient example of movable type.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Where commuters walk through remnants of an ancient Greek necropolis.

Go inside to really appreciate this 500-year-old technological masterpiece.

Pilgrimage site for star-crossed lovers.

South Korea's only sex-themed park.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

Site of a classic 19th-century physics experiment to prove the earth is rotating.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

The beautiful baroque library of the Hapsburg empire.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.