In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

A reproduction of earth's many biomes.

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

An urban forest overtakes what was the greatest failure of utopic urban housing.

An abandoned concrete jungle surrounded by a lush park.

This mosaic-covered bar is brimming with curated curios.

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

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

Less a museum than a bizarre fantasy world created by artists and engineers.

European castle ruins in an American state park are actually the product of death and grief.

The house is an iconic pilgrimage site for fans of the Illinois-based emo band.

The only place in America where anyone who wants can shovel coal aboard an antique train.

First known as the "Sample House," this construction mash-up was meant to be a living catalogue of building styles.

What was once the second largest steel mill in the US is now a sprawling complex of modern ruins.

A little-known subterranean street runs under some of the best-known buildings in Chicago's River North.

River pirates, murderous bandits, and serial killers used this Illinois cave as their debauched hideout.

This $3 million model train takes you through Chicago, Seattle, and the thousands of miles in between.

An innovative attempt to break a siege in the American Civil War still scars the earth today.

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

The narrowest house in America is seven feet of pure spite.

Bubbling up from deep underground is the warm crystal clear water that fills the Warm Springs Pools, America's oldest spa.

Nine of the very few concrete ships ever made in the U.S. are beautifully decaying off a Virginia pier.

This once-palatial plantation may have been the site where a draft of the Declaration of Independence was written.

The flower-shaped temple in Virginia aims to transcend the boundaries of the world’s religions.