A layered tribute to the work of mosaicist Isaiah Zagar.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Rippling sand dunes frozen in the Arizona rock.

A crumbling hospital from the 1850s on Roosevelt Island.

A man-made island in scenic San Francisco Bay.

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

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

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

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

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

The site of a concentration camp where inmates were made to take part in one of the largest counterfeiting operations in history is now hauntingly empty.

Berlin's old airport.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

Frida Kahlo's childhood home, now a museum of her life and works.

A museum in the former home of Marxist revolutionary Leon Trotsky.

66,000 pieces of art, donated by one of the world's richest men.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

The statue of John Harvard isn't actually John Harvard—or even, technically, the founder of the school.

A former waterfront market is now in the center of town due to some interesting Boston engineering.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

A terrific purveyor of natural history objects and curios.