Loftily flanking the mouth of Sydney Harbour are the rugged sandstone cliffs of North Head and South Head, providing spectacular viewing points across the calm water to the city 11km away, where the Harbour Bridge spans the sunken valley at its deepest point. The many coves, bays, points and headlands of Sydney Harbour, and their parks, bushland and swimmable beaches are rewarding to explore. However, harbour beaches are not always as clean as ocean ones, and after storms are often closed to swimmers. Finding your way by ferry is the most pleasurable method: services run to much of the North Shore and to harbourfront areas of the eastern suburbs. The eastern shores are characterized by a certain glitziness and are, fundamentally, the haunt of the nouveaux riches, while the leafy North Shore is largely the domain of Sydney’s old money. Both sides of the harbour have pockets of bushland that have been incorporated into Sydney Harbour National Park, along with several harbour islands: Cockatoo Island, the largest and easily reached via Sydney Ferries; Shark Island, a popular picnic destination, former penal site Fort Denison and Goat Island, site of a well-preserved gunpowder-magazine complex, all visitable with the Matilda or Captain Cook cruise companies; and Clark Island and Rodd Island, reachable by private vessel only.