I did drive through the salt flats of Utah, which were more flat and featureless than driving through Nebraska, but in that case it takes it to such an extreme level that it becomes surreal and a bit mesmerizing. When you can't tell the difference between Earth and sky, the landscape and the horizon and the atmosphere all bleed and blur together in a blinding white haze with one perfectly straight black line extending out in front of you seemingly into infinity, slowly disappearing into a shimmer, like driving into the twilight zone. So I feel like Iowa/Nebraska are at the absolute lowest point of being flat, featureless and monotonous until you get to the point where it becomes so extreme that it loops around and becomes interesting again. What's North Dakota like? I've been to South Dakota.