Apparently, there's not much to do during Minnesota winters (I kid), because Roger Hanson has been making gigantic ice castles in his spare time. Seriously, they're ginormous. We're talking 20 metres high and 26 metres long humungous beasts of man made nature. How does he do it?
His system is pretty ingenious. He sets poles to his design in November to frame the castle and uses cold water (about 37 degrees) from his geothermal heat pump to shape it. Hanson has a computer program that reads weather forecasts and controls when cold water will spray the frame to "grow" the ice castle. The sprayed water freezes when it hits the poles, thus forming these amazing ice castles. [Inhabitat]
This is Hanson's current beast.
This is an ice castle from humbler beginnings (2008).