I was watching Mythbusters recently where they tried to light a fire using ice as the focusing element.  It was pretty cool (no pun intended) to watch as they were finally successful.  The big hurdle being that the hot sun was obviously going to melt the ice, diminishing the focal strength of the 'lens'. 

Well Matthew Wheeler responded to the source of the Mythbusters' trials, Scientific American.  He found the results weren't that difficult at all, and he wanted to take things to the next level.  So he decided to make a lens out of ice that he could use to actually take photographs.  The link below shows some of the impressive results he achieved.  The clearly, non-winter shots are the ones that impress me the most.