One famous wadi is Wadi Feiran. It's located in Egypt. From looking at the pictures of this wadi, it was at one time a huge river. I got to see it last year on my trip there.
It is described in the Old Testament, and this is where Moses supposedly struck a rock and a fountain of water emerged from it.
There is an oasis there with ruins of ancient buildings and palm trees.
Visitors are warned to be careful because during a rainstorm, a wadi can fill with water and cause a flash flood .