Tassili n'Ajjer is full of natural rock art galleries. People have painted on these stones for at least 12,000 years - long before any kingdoms or pyramids existed. There are thousands of paintings, and scientists are still finding more.
The most surprising paintings show animals that don't live in the Sahara today - giraffes, elephants, hippos, crocodiles. That tells scientists something amazing: the Sahara used to be green. There were grasslands, rivers and lakes here. The desert we see today was once a wetland.
Over thousands of years, the climate slowly changed. The rivers dried up, the grasslands turned to sand, and the animals moved south. The rock paintings stayed behind, like a photo album of a Sahara that doesn't exist any more.
Today, the only way to reach the most famous paintings is to hike for several days through the desert with a guide. People who go say the air is so clear and the silence so big that they feel like they have stepped back in time. Tassili n'Ajjer is one of the most important rock art sites in the whole world.