When from Errachidia you keep on driving south for another hour, you´ll be in Rissani (it definitely is on your way if you want to go to Merzouga to see the desert).
I would really recommend a stop here, because it´s an important historical point. Back in the XIV-XVIIIth Centuries, Rissani was called Sijilmassa and it was a very important capital of the desert. Here people would commerce slaves, gold, spices and other products sold by nomad merchants.
Now the city is very dusty and not that beautiful, but there are two places where you absolutely need to go:
- the souq, where you feel like traveling back in time (Tuesday, Thursday and Sunday)
- the beautiful Zawiya Moulay Ali Ash-Sherif (free entrance, open from 8 a.m. to 18 p.m., non-Muslims can visit)
Zawiya Moulay Ali Ash-Sherif is a big yellow shrine built as a tribute to the Alawite dynasty´s founder who, as you can imagine, was called Moulay Ali Ash-Sherif. The moment you enter the building, you are transported to another place: you leave outside dust and chaos, and find beauty, geometry and perfection.
I just took some pictures out of respect of the people praying, but you can get the idea of how stunning it is. The attention to the details is incredible and you can really find peace just sitting on a bench and listening to the silence.