The only geyser in the state of Pennsylvania is caused by pressure from an abandoned coal mine outside of the ghost town Centralia.

Board a mine car and descend the #190 slope 300 feet underground into the Clark Vein of coal.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

This four-story steel sphere in Maryland was used to test biological weapons.

This general store is more than a century old and home to various oddities and antiques.

A monument marks the location of the first successful steamboat demonstration.