An open-air museum (also frequently open air museum) is a type of museum that exhibits collections of buildings and artifacts out-of-doors. They are also frequently known as museums of buildings or folk museums. The concept of an open-air museum originated in Scandinavia in the late 19th century and spread widely. A comprehensive history of the open-air museum as idea and institution can be found in Swedish museologist Sten Rentzhog's 2007 book Open Air Museums: The History and Future of a Visionary Idea.