A playground is an area designed for children to play freely. Modern playground often have recreational equipment such as the see-saw, merry-go-round, swingset, slide, climber, walking bridge, jungle gym, chin-up bars, sandbox, parallel bars, overhead ladder, trapeze and trapeze rings, playhouses, and maze, many of which help children develop physical coordination, strength, and flexibility, as well as providing recreation and enjoyment. Common in modern playgrounds are "play structures" that link many different pieces of equipment.