Jane points us towards this Metafilter discussion about badgirs (or barjeels) - towers topping buildings in the Mideast which catch the wind, cooling the air as it moves down through the tower and providing passive air conditioning. It turns out there are a bunch of passive cooling devices. You can, for example, build a passive refrigerator for food or medicine out of two appropriately-sized clay pots with a layer of wet sand between them. There are all sorts of tricks for building passive cooling homes in hot climates. You can even pump water passively. Why work, when solar energy or gravity will do the job for you?
this is a set of instructions for airconditioning that supposedly was used by the romans: http://www.i4at.org/surv/aircond.htm
Wow. That's sooo cool. Thanks, Rebecca!