I'm experimenting with the Kayak RSS API to keep an eye on the cheapest destinations during particular periods in which I'm able to travel. When reading the RSS feed, you can optionally supply a "trip idea id" which, I think, controls the region(s) that are searched for cheap fares. If you don't specify you get the "Kayak top 25" feed. Unfortunately, although this API is public, I can't find a list of codes and what "trip ideas" they stand for. Does anyone have any experience with this API?