Have you been looking for something other than a traditional cache? You say you're searching for something just a little bit more challenging? Then you need not look any further than this one. I have just the multi that you have been looking for....except it really isn't very challenging. In fact, it's the easiest multi that you'll find in Mason City.
There are two stages for this multi, and you're looking for something about the size of a micro at each of the locations.