A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

Huge masonic hall in Philadelphia with lavishly themed rooms.

This elaborate towering structure was once famed for its revolutionary height.

The first American department store, and home to the largest operating musical instrument in the world.

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

A museum dedicated to the strange and extravagant costumes and memorabilia of the mummers, a tradition older than Philadelphia itself.

One of the oldest of its kind.

The fastest transatlantic ocean liner sat abandoned in a Philadelphia shipyard for decades.

A girls' boarding school inspired by the Chicago World's Fair, once abandoned, now restored to strange and scenic glory.

The tallest The Church of Jesus Christ of Latter-day Saints temple in the world soars above the Beltway.

An astounding collection of medical specimens, including bits of President Lincoln.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

Giant acorn-shaped 19th century gazebo from which suburban Washingtonians gazed upon the original "silver" spring.

A benevolent, 16-foot-tall river dragon lives on a suburban lawn.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 years.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

An obscure federal monument honors the French diplomat who served as Ambassador to the U.S. during WWI.

At 207 feet, one of the world's longest continuous escalators.

Parking garage where Bob Woodward met Watergate source "Deep Throat."

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.