This hidden stream beneath Indianapolis makes an appearance in the best-selling novel "Underground Airlines."

The site of a 19th century "dream city" that almost rivaled Chicago before being swallowed by the Indiana sand dunes.

A stunning, abandoned limestone quarry in southern Indiana provided the stone to erect the Empire State Building.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

This marker identifies the location where three states converge.

This massive home was constructed by one of the greatest conservationists in Colorado history.

This now-abandoned outcrop is an important Native American spiritual site, overtaken by European settlers and mining pollution.

Once a lonely sentinel on the edge of the Great Plains, this rebuilt trading fort offers a glimpse of life on the Santa Fe Trail.

One man's love for East Coast diner culture brought an entire eatery all the way from New Jersey to Colorado.

The remains of a World War II-era Japanese American internment camp dot a windswept Colorado hill.

An enthusiastically interactive mining museum that won't let black lung ruin the fun.

A prehistoric rock shelter that's literally in someone's backyard.

A stark reminder of the huge nuclear weapons plant that once stood on the site and its effect on the surrounding area.

Climb to the top of this spiritual tower, and you'll be rewarded with spectacular views.

This razorback ridgeline has doubled as a scenic drive since the early 1900s.

Travel through the wholesome amusements of yesteryear at this charming miniature village.

A small horde of mythical creatures lurk almost imperceptibly within the museum's wildlife dioramas.

The clock that sets them all.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

One woman's UFO-themed campground, complete with self-built energy vortexes, UFO-themed weddings, and magic bushes.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

When ecosystems collide in the arid Southwest.

Hidden beneath a bridge, this waterfall is known for the large amounts of graffiti painted on its base.

This "zoo" is a cross between a junkyard and a sculpture garden, featuring animals you won't see anywhere else.