An open-air museum is a museum that is outdoors. It usually has replicas of buildings, objects, and places from the past so that people can visit and learn about the history of different places and times. People can walk around the museum and see things from the past up close, like old homes and shops. This means they can learn a lot more than they would if they only read about history in a book or watched a movie. It's like taking a walk through history!