Igloos and Ice Hotels (from http://www.lib.uaa.alaska.edu/archives/Photographs/FavoritePhotographsImages/EskimoIgloo.html) Igloos have served native people in the Arctic as shelter for thousands of years. They are built with snow and ice. For insulation and strength purposes two layers of ice are necessary after the structure is completed. While the sun melts a tiny layer on the outside of the igloo and creates a water layer that refreezes at night, the inside takes a bit more work. The entrance is sealed off, a heat source is placed inside and the snow begins to melt after some time. Once all the walls are wet, the door is opened and the sudden exposure to the cold creates another layer of ice on the inside. After this treatment an igloo can withstand the weight of a polar bear. At least according to legend. An ice hotel is nothing but an oversized igloo - with a bunch of fancy artwork thrown in. Reinforcing frames are used to meet building requirements and keep the humungous structures from collapsing. While the Chena Hot Springs version had refridgeration tubing inside the walls to allow for year-around operation, all other ice hotels in Canada and northern Europe rebuild their structures every winter and let it melt down in the spring. A short description of how the construction of these hotels is being accomplished can be found here. (from http://www.cnn.com/2003/US/West/11/29/ice.hotel.ap/)   (from http://www.arctic-experience.co.uk/tour22w/index.htm)     And as an example of the strength of these structures, the photo below shows an igloo that made it into the Guiness Book Of Records: (from http://fy.chalmers.se/~kuzmin/HOBBY/IGLOO/record-sm.jpg)