The world's largest man-made underground caverns offer unparalleled underwater wonders.

The famous author's birthplace is preserved in a town that he once described as narrow-minded.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

This whimsical Oz-themed park had a wonderful impact on the surrounding neighborhood.

The only Bahá'í house of worship in North America and one of only a handful worldwide.

Lie in a hammock where George Washington stood.

Now abandoned, the first public health hospital in the U.S. saw more than one million immigrants from around the world.

A discreet little stairway on St. Nicholas Avenue leads to a quaint and unexpected cobblestone street of 19th century wooden rowhouses.

A crumbling hospital from the 1850s on Roosevelt Island.

One of only two commuter aerial tramways in the United States.

A walk through the historic city center, under the streets of Seattle.

This former coal gasification plant found a curious second life as a popular public park.

A Roman-style column in Oregon hides a spiral staircase inside.

100-year-old shipwreck you can walk up to at low tide.

The second seat of Nye County, still mostly a ghost town, has become a magnet for those looking to live "away from it all."

The only thing still moving in this town is the eponymous hot spring.

An eatery for UFO seekers on the Extraterrestrial Highway.

This sign designates the road that leads to the infamous Area 51.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

The precious-metals strikes dating back to the 1860s are now mostly inactive, but this area has become the United States' only domestic source of lithium.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

Odd outsider art installations surround a Gold Rush-era ghost town.

The most magnificent bottle house in a town strangely full of them.

This crumbling Death Valley mining complex was known for its use of giant, 20-mule team wagons.