Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

This Dutch Colonial home is the oldest remaining farmhouse in Manhattan.

Years of archaeology, just chillin' by the water cooler.

A suspended garden, now gone, once hung in the middle of this abandoned church.

But did the famous feminist and abolitionist ever really say those iconic four words?

These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

Andy Griffith's hometown has made itself up to look like the fictional town of Mayberry.

A 300-ship graveyard, with a few still visible at low tide.

This humble star-gazing center touts itself as the "Birthplace of American Astronomy."

All of Chicago's wood-paved streets are long gone but two alleys remain.

A Nesting Doll of Churches.

The legendary building that needed ghostly approval before being built.

The only visible piece of San Francisco's most famous shipwreck.

This partially buried wreck is one of the most complete of its kind but is only revealed when the sea allows.

A Barbary Coast watering hole built into a Gold Rush shipwreck.

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

A 140-year-old castle with underground caves hidden in San Francisco.

The United States Capitol's former columns still stand.

The largest earthwork effigy in the world.

The subtle science of a master molecular gastronomist.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

Gold Rush ship-turned-hotel buried underneath San Francisco's financial district.

Politicians, bureaucrats, and military officers gathered in this field near the Capitol to settle their disputes with blood.