You have the Adirondaks and surrounding areas. Other than that, it's not that difficult. OH, IN and IL are easy terrain-wise. There are some big rollers in IA, but no mountains. MN is relatively tame, too. The real challenge in OH, IN and IL can be the heat and humidity. Corn does not provide shade.

I haven't done the new routing in ND. (AC changed the old route due to the oil boom in the NW part of the state.) However, I did do the old route and a supported tour in ND that went through Bismarck. Generally, you get relatively flat to sweeping rollers with not much that is too steep. Again you have the lack of shade to deal with. And if you get a nasty ND headwind, you can get worn down quickly. During the supported trip we rode for two hours at a 9 mph average over gently rolling terrain. In a tuck going down hill it was hard to get over 13 mph.

Note that the NT goes through Cleveland. Don't be scared. I found it enjoyable. The optional tour of the Emerald Necklace was well worth it. The houses in Cleveland and Shaker Heights were pretty cool.