The U.S. Supreme Court's secret Cold War relocation facility in the mountains of North Carolina.

The highest point in North Carolina and the United States east of the Mississippi River, Mount Mitchell is named after argumentative explorer Elisha Mitchell.

The highest point in Tennessee, Clingmans Dome bears witness to the ravages of one type of insect.

One of the largest trees of its kind in California.

This hidden gem of a garden has one of the only surviving Victorian ferneries in America.

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

A bit of retro transportation flair preserved in the world's largest department store.

An ancient underground cultic temple where sunlight penetrates on the summer solstice.

A rare tour of a commercial jet assembly plant, held inside one of the largest buildings in the world.

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

The original vault that held the president's remains still stands, empty, not far from where he was finally buried.

You can walk through the first Boeing Air Force One, which famously carried JFK's casket from Dallas back to D.C.

A quiet, gothic haven nestled between Pittsburgh's Squirrel Hill and Point Breeze neighborhoods.

This innovative steam machine was no doubt the most famous of the pioneer locomotives.

The massive machine creates cracking displays of indoor lightning.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

Ship-sized kinetic sculptural fantasy.

London's Victorian Tower of Babel.

The broken skateboards that became a poignant memorial to a murdered skater.

London's smallest police station is barely the size of a phone booth.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.