Aigues-Mortes belongs to the Camargue area.
The historical centre is all contained within a compact area of the city walls, easily explored on foot.
Walk around the ramparts of the medieval city walls, and see inside the various towers, including the Constance Tower. This costs money, but it's worth the price. The ticket office, located in the North West corner, offers audio guides, but is closed at lunchtime. It's also possible to visit the Salt works of Aigues Mortes.
Lots of shops selling tourist nick-nacks
There are many pleasant cafes and restaurants within the city walls, particularly around the central square.