There's always the "big" items which every one knows about. You know, Mammoth Cave, Disnyland, Mount Rushmore. But for every thing else, you just have to search. The internet is your best friend to scope out attractions along your route. Punch in any search engine the name of a town or city you are passing, and jump to the "tourism" information. More stuff will come up than you can possibly ever have time for.
There are certain things I enjoy, and have a couple books, specific for "Indiana".... Weird Indiana (but the Weird America series is now in almost every state too). And books on little unknowns about Indiana. Another favorite attraction for me are "Ghosts and UFO sightings". And there are thousands and thousands of "hits" you'll get on the Internet for just about any location you plug in.
Another way to find a subject that is interesting to YOU, is to stoop at Road Side rest stops or Welcome Centers on the interstates and pick up the fliers and brochures on display.
Sometimes, you just have to take an exit and see what's there. I don't think there is an easy way, and it all depends upon your own interests.
We also really enjoy road side fruit and vegetable stands. Sometimes they really have some unusual items for sale, more than food. So we are always watching for these stands.
