On last weekend's motorcycle ride, one stop along the way to Winslow, AZ, was Tonto Natural Bridge State Park.
Believed to be the largest natural travertine bridge in the world, it stands 183 feet high over a 400 foot long tunnel that is 150 feet at its widest point.
A prospector named David Gowan stumbled upon the site as he was chased by Apaches. He hid for two nights in a cave within the tunnel. He later claimed squatter's rights.