I've always took this to mean that Lyme doesn't have a wide avenue or boulevard type street that other spa cities did. Brighton, for instance, has the Marine Parade, a wide street designed for lots of traffic with an adjoining promenade for walking. Other spa cities have had roads designed specifically to deal with traffic and large numbers of people. Lyme doesn't have that - it remains as it ever was, with its steep, windy roads running down to the water. It has not been "developed."