This temple, built by an eccentric religious leader before his death, sits guarded and in ruins.

Carved by a waterfall in a hard-to-reach rock formation, this heart-shaped rock has inspired romantics for decades.

A mysterious shape catches the eye in this 16th-century painting.

Washed out by the Johnstown Flood in 1889, the surviving portion of the original two-span bridge now resides at Fishing Creek.

Taking the subway here means doing so over a bridge located in the middle of an estuary.

With over 10,000 lights, this engineering marvel lights up the city after dark.

This ancient stone bridge dates back to the early Middle Ages.

This museum looks at the history of one of America's most famous prisons and most beloved albums.

This 19th century hydroelectric powerhouse was the first of its kind.

This former boomtown "island" is now submerged below Folsom Lake.

Dentist's hated concrete colossi are now beloved icons of the community.

The tallest bridge in California was constructed for a project that was eventually cancelled.

Rifle through images of skyscrapers, Worlds Fairs, and more in the largest public postcard repository in America.

This public library and its impressive collection of academic books have not changed since the 17th century.

This medieval manuscript collection has some of the most obscure and ancient texts in the world.

The world's tallest boat lift stands as a massive piece of industrial tourism.

The tiny Belgian town's ancient version of Mardi Gras involves eerie wax masks, sticks for warding off evil, and ostrich plume hats.

A visionary precursor to the Internet made of index cards.

A 141-foot wave of crashing lumber guards the entrance to the Grand Place in Mons.

Petting this mysterious iron monkey supposedly brings good luck.

This exhibition space designed to look like the skeleton of a whale is hidden underground.

A southern Swedish island is home to the last ERSTA artillery battery, meant to protect the shoreline during the Cold War.

Stunningly detailed mosaics in a New York subway station bring life to the Weimaraners of artist William Wegman's work—and to thousands of commutes.

The curious underground history of keeping Paris clean.