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

A secretive collection featuring objects that were designed specifically for U.S. intelligence operations.

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

A monument marks the location of the first successful steamboat demonstration.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

An 18th-century Spanish watchtower made entirely of seashell and concrete.

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

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

Concrete strongholds stand guard over the Golden Gate.

A giant Troll lurks under one of Seattle's oldest bridges.

Statue of Lenin, from Cold War era Czechoslovakia, now in a neighborhood of Seattle.

A museum dedicated to the history and exploration of both popular music and science fiction.

A wall of chewing gum moonlights as collective art.

This blowhole is supposedly caused by a trapped monster.

These ancient sacred grounds granted amnesty to those who managed to reach them.

A tunnel of hardened lava along Maui’s famous Road to Hana.

An authentic replica of an Asian temple and garden hidden amongst the natural beauty of Hawai'i.

Take shelter from Hawai'i's tropical heat under the massive canopy of largest Banyan tree on the island.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

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

The United States Capitol's former columns still stand.

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.

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