If you've ever gone to a hot destination and found, to your despair, a weak or absent aircon, then this is for you. Even opening the window might not be enough in humid climates, so here's a quick tip. First, you'll need a towel and some cold water. Simply soak the towel in a cold bath and strain it. Next, lie the damp towel over the edge of the window. When the breeze comes, it'll be cooled by the towel.
Make sure the window is slightly ajar, and you don't hang the towel too far out. Ideally, fold it over a few times and leave it on the inner windowsill.