Fears of Satanic worshippers swirl around five Celtic-inspired megaliths.

The largest underground pedestrian tunnel system in the U.S. mostly caters to the people working in the offices above, but provides a great, air-conditioned way to traverse the city.

An immense cave that has served as an outlaw's treasure trove, an underground dance hall, a nuclear fallout shelter, and much more.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

A modernist landscape of water and sci-fi concrete.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.

An emerald-green grotto just a short trip from Austin.

An out-of-the-way state park in Oregon that features both a picturesque waterfall and the ruins of a hydropower plant.

Get your cosplay on at Portland’s only Medieval fantasy-themed mead hall.

A puppeteer’s paradise offering shows, workshops, and an archive of over 2,000 puppets.

According to legend, this rock represents a young girl trapped by an evil ocean spirit.

Along the Outback Scenic Byway, adjacent to hot springs, this human-made geothermal feature takes unexplained breaks.

Railroad came. People came. Railroad left. Town died.

The first full-scale tunnel built in America is short but scenic.

This tiny 19th-century tunnel was built so a man could move his cows from one field to another.

An ancient cave system in Tennessee’s Appalachian foothills converted to a 1,200-person music venue.

Pennsylvanian mass grave and possibly mass murder.

Hellam Township is reputed to feature seven remote gates, which when passed through in the right order, open an entrance to hell.

Over 100 concrete munitions bunkers are all that remain of a Pennsylvanian village seized by the US government.

This historic old movie house was the scene of one of the Blob's most iconic attacks.

The only way to see Pittsburgh is from the top of this lookout point, just like the ancient members of the native peoples did.

Behold the rickety wooden glory of the world's oldest operating roller coaster.

The United States’s oldest funicular railway glides up and down a steep Pittsburgh street.

Erected in 1697 this Philadelphia bridge is the oldest surviving roadway bridge and perhaps the oldest stone bridge in the United States.