. He once told the class, "I want to be drinking in a snow bar by Friday." His students went outside and got to work, and sure enough, "we had 50 people inside the snow bar by Friday afternoon."Sijpke is originally from Holland, where water is usually found in liquid form. So when he moved to Canada, he was fascinated by snow and ice. To him, frozen water is a fantastic (and free) building material. He's built some seriously impressive structures out of snow and ice—including a 1/5-scale model of the Roman Pantheon. The 32.7-foot tall, 32.7-foot diameter structure was made from 400 tons of snow. More than 125 McGill students and faculty squeezed inside its walls, which were four feet thick.

So Popular Science asked Sijpke how to build an igloo. "Scientifically, the best way is how the Inuit in the North still do it," he says. "They lay snow blocks in a spiral."