This natural wonder is located in Silver Falls State Park in Oregon. I think that it is specifically the 177-foot South Falls, one of the 10 waterfalls in that park. Photographer Jared Decker climbed inside a cave behind the waterfall and snapped three shots, which he stitched together into this beautiful image. It is as if Nature herself has an eye and she gazes back at you.
You can buy a print of this photo at Fine Art America.