My favorite random prerequisite class from undergraduate days? Geology of the National Parks.
One project, in between geology lessons based on pretty pictures, was customizing a geologic map of the amazing United States of America. I added, in red lines, the path of my travels.
But that was almost ten years ago - yikes - so when I found it in the way-back of my closet while cleaning/packing, i decided to update it before ceremoniously burning it in the wood stove. In sharpie, the places i've explored since Fall 2001.
The noticeable yet-to-explore areas of our country? California and Oregon, Texas, and the Northeast. All will come in time.