More than five thousand known Aboriginal art sites cover the walls of Kakadu’s caves and sheltered outcrops, ranging in age from just 30 years old to more than 20,000. Most of the art sites are of spiritual significance to Aborigines who live in the park, and only a few locations, such as Ubirr and Nourlangie, can be visited by tourists. The paintings incorporate a variety of styles, from handprints to detailed “X-ray” depictions of animals and fish from the rich Estuarine period of six thousand years ago. At this time, rising sea levels are thought to have submerged the land bridge by which Aborigines crossed into Australia. It’s not unusual to see paintings from successive eras on one wall. Contact period images of seventeenth-century Macassar fishing praus and larger European schooners might be superimposed over depictions of ancient Mimi spirits or creation ancestors. For the indigenous people, the art sites are djang (dreaming places), depicting Dreamtime stories, and the images serve as prompts to communicate valuable lessons that are still passed down from generation to generation.