UPDATED 12 July 2010 to include more information about 'Hippo Packs'
Welcome to summer, Korea style. It's called 장마철 (rainy season), although you might call it the rainy season, the monsoon season, or that *#@%! hot season. Whatever you call it, there are more than a few ways to beat the heat.
Step one: turn off the heat. If your apartment has ondol heating (and virtually every Korean apartment does), there may be a switch to go from 'winter' mode to 'summer' mode. In the former (겨울, or winter), the ondol system turns on the hot water and heats up the floor; in the latter (여름, or summer), the ondol system only heats up the water.