Minnehaha Falls in Minneapolis, Minnesota - in the winter, the falling water slowly freezes creating some massive ice formations - this is what it looks like if you climb up behind the ice wall.
More than you probably want to know:
Minnehaha Falls was the inspiration for Henry Wadsworth Longfellow's poem 'Song of Hiawatha' although he never actually visited the area. A life sized bronze statue of the main characters of that poem, Indian leader Hiawatha and his wife Minnehaha, stands at the top of the waterfall.
Check out this awesome 360 degree panorama view of the place made by Ed Fink: bigeyeinthesky.com/NewPan/Assorted/MinnehahaFallsIce.html