Chicago's Navy Pier on Lake Michigan was a training hub for aircraft carrier pilots during WWII.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

10,000 flowered plants bloom in the City of Roses.

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

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

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

Golden Gate Park's historic collection of plants.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

L. Frank Baum wrote part of the "Wizard of Oz" series in this wooden Victorian beach resort.

San Diego's most historic and haunted home.

The last bastion of Roman presence north of the Alps looms over a German town.

A striking 12th-century-style castle built on the edge of a cliff.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

At first glance, this area seems like just another city park, but the lush landscape hides a dark past.

The world's most active stratovolcano is almost always erupting.

These imposing walls and towers look more like the ruins of a fortress than a monastery.

Thousands of well-dressed mummies below a monastery.

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

This Ukranian fortress is one of the best-preserved medieval castles in Europe.

340-foot statue built to honour the Heroes of the Soviet Union.

The site of a tragic massacre that spawned a multimedia franchise.