Depends on what one likes to do.
We like caves, natural history museums, art museums, living history museums, aquariums, botanical gardens, wildlife refuges, oceans, lakes, rivers and places the dog can go with us. I like to add a restaurant to the mix (onlyinyourstate is my best source along with google maps.... high star count with lots of reviews is the tipoff to a good local restaurant). We also like places that are not wall-to-wall people. We don't care for shopping or drinking.
For locations, I like to look at onlyinyourstate.com and pinterest as a starting point. I use mymaps (google maps) to create a state map filled with places I find interesting. I add nearby campgrounds/rv parks and restaurants to the mix.