The three-hundred-mile stretch of I-90 through southern South Dakota is vast. Really, really vast. Until and unless you reach the Black Hills and the Badlands to the west, the flattened landscape across the central and eastern portions can lose their visual novelty to even the most innocent traveling yokel after about the first five or ten miles. Roadside attractions blessedly break up that monotony here and there — some ironically and some with utmost sincerity. It’s more rewarding when you feel compelled to stop for the sake of art appreciation than out of car-happy desperation.