23.  Mega Zips, Kentucky

Mega Zips is the planet’s only totally underground zip line course. It is situated in a huge hollowed-put 100-acre limestone quarry now known as the Louisville Mega Cavern. The cavern is so large it stretches out under sections of the Louisville Zoo and the Watterson Expressway. Here you can fly through the air as high as 70 feet on this exciting underground attraction.

24.  Emerald Cave, Arizona

You will find the Emerald cave a mere 45-minute drive out of Las Vegas in the as yet unspoiled Black Canyon. Veteran visitors say this cave is the true highlight of the canyon with its striking sparkling green waters. Here you can go kayaking in the calm cove’s water or escape the glaring sun by paddling into the caves that run through the cliff face.

25.  The City Hall Subway Station, New York

Finally, you’ll wonder why the other New York subway stations are so drab-looking once you see this place. This abandoned City Hall subway station comes complete with chandeliers, a vaulted tile ceiling, and leaded skylights. Opened in 1904 this station was shut down in 1945 because of its short platforms. Ah, but you can still see this outstanding spot thanks to tours offered by the New York Transit Museum.