The main island of Singapore is shaped like a flattened diamond, 42 km (26 miles) east to west and 23 km (14 miles) north to south. Near the northern peak is the causeway leading to West Malaysia—Kuala Lumpur is less than four hours away by car. It is at the southern foot where you will find most of the city-state’s action, with its gleaming office towers, working docks, and futuristic "supertrees," which are solar-powered and serve as vertical gardens. Offshore are Sentosa and over 60 smaller islands, most uninhabited, that serve as bases for oil refining or as playgrounds and beach escapes from the city. To the east is Changi International Airport, connected to the city by metro, bus, and a tree-lined parkway. Of the island's total land area, more than half is built up, with the balance made up of parkland, farmland, plantations, swamp areas, and rain forest. Well-paved roads connect all parts of the island, and Singapore city has an excellent, and constantly expanding, public transportation system. The heart of Singapore's history and its modern wealth are in and around the Central Business District. The area includes the skyscrapers in the Central Business District, the 19th-century Raffles Hotel, the convention centers of Marina Square, on up to the top of Ft. Canning. Although most of old Singapore has been knocked down to make way for the modern city, most colonial landmarks have been preserved in the CBD, including early-19th-century buildings designed by the Irish architect George Coleman.