In Europe they're called sculleries; in North America, dirty kitchens. Whatever the name, these rooms allow you to segregate the messy aspects of food prep from your eat-in kitchen -- a big selling point for people who entertain a lot.

Often connected to the main kitchen, a dirty kitchen is generally smaller. Inside you put the gear you don't want guests to see: a second oven for sauces that spatter and bubble, a counter for slicing, a king-size sink, garbage cans and a door so you can take garbage out easily. You can make all the mess you want -- and just close the door when the guests arrive.