One of the houses I clean at work isn't air-conditioned. (Actually, several houses are like that, but I've chosen to focus on one in particular.) The house has a swamp cooler, which does a tremendous job at cooling the building, so long as you're standing directly underneath the swamp cooler. Since most places in the house can't be accurately described as "directly underneath the swamp cooler" (except for a certain chair that I make a point of sitting in when I'm winding up the cord to my vacuum), being in that house is generally a less than pleasant experience.
I'm not quite sure how swamp coolers work, but I know that they manage to make the inside of the building they are trying to cool very humid, a feat which is especially impressive in Utah. Forget buying a humidifier. Just install a swamp cooler in your building and you're set. It has the benefit of also making your house slightly cooler (but only in the same sense that cerulean is slightly bluer than teal).
While vacuuming the aforementioned house, I walked into a room with a particular smell in it. My memory is particularly sensitive to smells - certain smells are associated powerfully with various events in my life. Sometimes it works the other way - I was sitting on my couch this morning while waiting for dimmi to come and visit me, and I could have sworn that I smelled Petra. (It's a good smell, Petra. Don't worry.) This immediately invoked a whole series of tender memories that I had to quickly turn to my book to suppress, lest I get caught up in half an hour of reminiscing. At any rate, this particular smell recalled memories, but it wasn't a strong or recognizable enough scent that I could place the memories. I just had vague recollections of something pleasant in my past. For a fleeting moment, I saw myself in front of a TV with my family while watching a movie, but I couldn't get any more than that.
I left the room and tended to other things in the house for a few minutes. In time, I came back to the room, only to smell the same odor. This time, however, I noticed a few broken-down cardboard boxes leaning against a desk. Immediately, the smell made sense. I was smelling slightly wet cardboard (from the swamp cooler, which was making everything humid). The memory made sense, too. The missing element from my memory was pizza, which we were all eating out of the delivery box. The pizza, containing moisture, had made the cardboard in the boxes damp, creating a similar smell to the one I was currently experiencing.
Apparently I associate the smell of slightly damp cardboard with memories of eating pizza as a child. I just keep learning interesting things at this job.