Its cultural attraction can be attributed to its cultural diversity that reflects its colonial history and Chinese, Malay, Indian and Arab ethnicities. It is also environmentally friendly, and maintains natural and heritage conservation programs. As English is the dominant one of its four official languages, it is generally easier for tourists to understand when speaking to the local population of the country, for example, when shopping. Transport in Singapore exhaustively covers most, if not all public venues in Singapore, which increases convenience for tourists. This includes the well-known Mass Rapid Transit (MRT) system. The Orchard Road district, which is dominated by multi-story shopping centres and hotels, can be considered the center of tourism in Singapore. Other popular tourist attractions include the Singapore Zoo and Night Safari, which allows people to explore Asian, African and American habitats at night without any visible barriers between guests and the wild animals. The Singapore Zoo has embraced the 'open zoo' concept whereby animals are kept in enclosures, separated from visitors by hidden dry or wet moats, instead of caging the animals. Jurong Bird Park is another zoological garden centred around birds, which is dedicated towards exposing the public to as much species and varieties of birds from around the world as possible, including a flock of one thousand flamingos. The tourist island of Sentosa, which attracts more than 5 million visitors a year, is located in the south of Singapore, consists of about 20-30 landmarks, such as Fort Siloso, which was built as a fortress to defend against the Japanese during World War II. Guns from the World War II era can be seen at Fort Siloso, from a mini-sized to a 16 pound (7 kg) gun. Moreover, the island has built the Tiger Sky Tower, which allows visitors to view the whole of Sentosa, as well as the Sentosa Luge, a small one- or two-person sled on which one sleighs supine and feet-first. Steering is done by shifting the weight or pulling straps attached to the sled's runners. Singapore has two integrated resorts which house casinos, namely Marina Bay Sands and Resorts World Sentosa