Is Merzouga really part of the Sahara Desert?

Yes — Merzouga sits on the north-western edge of the Sahara, and its Erg Chebbi dunes are a true Saharan sand sea.

The Sahara is a mosaic of stony plains, oases and sand seas (ergs), and Erg Chebbi is one of its genuine ergs. When you climb a dune behind the camp, the sand rolling to the horizon is the same desert that continues into Algeria and beyond.