Sahara desert

Thanks to underground rivers or aquifers, oases exist in the desert.

An excerpt from the article 22 facts about Sahara desert

These are largely relict, non-renewable bodies of water that date back to times when the Sahara had a much wetter climate.

In the central part of Algeria, there is a natural area about 160 kilometers long that contains a string of small oases. Several towns and numerous villages have been established there.