Going over the edge of Niagara Falls
You can walk up to the very edge of the Horseshoe Falls, to a point where the water is directly under you and the edge is a mere twenty or so feet away. It's very scary. I didn't see anyone with a barrel, though.
Aerial Photo of Horseshoe Falls (at Niagara Falls)
Aerial Photo of Niagara Falls (American Falls)
Aerial Photo of Niagara Falls (Horseshoe and American)
Picture of Niagara Falls (American Falls) with Rainbow
Picture of a Rainbow over Niagara Falls
Picture of the edge of Niagara Falls (with a Rainbow!)