The Walt Disney World Resort, also known as Disney World, is an entertainment complex in Florida, in the United States. Opened in 1971, the property covers nearly 101 km2, only half of which has been used. It is comprised of four theme parks: the Magic Kingdom, the Animal Kingdom, Epcot, and Disney's Hollywood Studios. It also contains two water parks, twenty-seven themed resort hotels, nine non-Disney hotels, several golf courses, a camping resort, and other entertainment venues. Today, Walt Disney World is the most visited vacation resort in the world, with average annual attendance of more than 52 million.