They lie all over the desert, in different stages of decay. Some have crumbled entirely, now nothing more than rubble. Others are on the verge of collapse, various sections already scattered in the sand. There are ones that remain mostly intact and it is these ones that the desert dwellers seek out. They provide better shelter than the ghost towns and are less conspicuous than the city. But the desert is harsh and has ensured that few of these structures remain. Legends abound of one perfect tower and one perfect fort that exist in the desert, but they have yet to found.
Some of these constructs are empty, some are inhabited by wildlife and some contain the remains of those who used them for shelter in their dying days.