Investigation and exploration are key skills for lifelong learning. Natural play develops these skills in children in a way man-made toys don't, as traditional toys and equipment are designed to be used as the creator intends, while nature has no such prescription.
Free play in nature allows children to discover more than the human mind can conceive, and no two children will play the same way and discover the same things in the same natural environment.
Children have a natural curiosity and interest in the environment, and it is so important that this is fostered by allowing them to explore as they desire and develop their own autonomy in the natural world.
Traditional games and prescriptive play can even be enhanced by a natural setting. Consider letting children play hide and seek in a set area of a national park or playground, or taking normal activities like craft or homework outside.
Children will adapt to environmental conditions and begin to experiment with different natural phenomenon, discovering how insects, weather, ground surfaces and even falling leaves effect their play.
Children can learn so much from having the freedom to discover what nature has to offer - so dig, climb, inspect, collect and investigate - and be sure to explore all the world has to offer!