Boiling River, Yellowstone National Park

Near the North entrance to Yellowstone park is a small parking lot. A trail from this lot leads to hot spring flow from Mammoth Hot Springs. Swimming is permitted here (as of summer 2007 at least). The water temperature ranges from hotter than one can stand to cold. Move around until you find the temperature right for you. Montana mountains can be seen in the distance.
 

Picture Specs & Equipment Reviews

70mm  f/11.0  1/100  ISO 100     Size: 4992W x 3328H  
 
Canon EOS 1Ds Mark II
Canon EF 24-105mm f/4 L IS USM Lens