The news that the Upper West Side's Claremont Riding Academy, a stable and horseback riding school at 89th and Amsterdam, is closing imminently after being sold to a developer—perhaps as soon as this Friday—is a blow not only for uptown riding princesses (just think how much more painful their virginity-losing will be!) but anyone else who enjoyed taking one of the horses out for a little Central Park wandering. As a correspondent reports: