Chattanooga — Barn roof billboards, a view of seven states, an underground waterfall and stunning fall colors have drawn tourists here for decades. But if all you’ve seen of Chattanooga is Rock City and Ruby Falls, well, you’re missing a lot. The riverfront downtown area, anchored by the Tennessee Aquarium, has enough diversions to keep the kids busy all day. A couple interested in art, natural history, shopping and good food will need more time than that.