The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

San Francisco's newly reopened hands-on science museum.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Scattered throughout London are ancient remnants of the city's former bounding wall.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

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

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

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

Museum devoted to the artificial language of Esperanto.

Handsomely crafted representations of our round planet.

The beautiful baroque library of the Hapsburg empire.

Antiques by the Bay.

A large instrument played by the wind.

A trail weaves through the verses of a poem illustrated by stone sculptures inspired by Native American pictographs.

Rodin's famous depiction of Dante's 'Inferno', amidst a sculpture garden of many of his other works.

The world's first permanently occupied mountain-top observatory continues to report on the stars.

An ominous concrete cube cuts a dystopian silhouette atop this California mountain.

A mysterious monument covered in a binary code marks the heart of tech.

A life-sized mammoth sculpture marks the spot where the remains of a Columbian mammoth were discovered in 2005.