There are two types of World Heritage Sites. The first represents cultural and the second natural heritage.
Cultural heritage sites have to show a masterpiece of human creativity or an important exchange of human values over a long period of time. This exchange must be seen in architecture or technology, the planning of the town or city and the design of the landscape. It has to show evidence of a tradition or civilisation that has disappeared or is still alive. It can also be a very good example of a type of building, group of buildings, use of technology or reflect important stages in human history.
A place where humans settled and used the land in a way that represents their culture can also be a cultural heritage site, especially if the area is affected by change that cannot be reversed. The authenticity and the way the site is protected and managed are also important factors.
Natural sites that can be considered to become World Heritage Sites must show major stages in the earth's history. This can be in fossils, rocks and how the land and natural features like mountains have been influenced.
If an area contains rare natural formations, like unique rock shapes, or is very beautiful, or has habitats and species of animals and plants that can only exist there, it becomes important to protect it. This also makes it a possible World Heritage Site. As with cultural sites looking after the place is very important.
Some special places fall into both cultural and natural heritage sites and in 1992 Unesco decided that places that show the relationship between people and their environment could also be cultural landscapes.