There are 2 things I want to do before I die. I dont know the type of people you are so neither may fit your bill.
1) (VERY COLD) Different parts of the world have them... But I want to do the one in Europe to give me a reason to visit a few other places... Anyway it's called the "ice hotel."
http://www.icehotel.com/ it's a hotel made completely of ice. I don't drink, but they have an ABSOLUT ICEBAR... Just in case. IDK it's just something I want to do.
2) (VERY WARM) There's this hotel in Coata Rica that's built in the trees (i.e. Swiss Family Robinson)...
http://www.costaricatreehouse.com/