So lets get the obvious out of the way colours, light and the whole atmosphre are great.
The name of the picture is "Desert Stronghold" so let's see what one can get out of this concept. It is "build into" the scenery makes it look very easy to defend. There is one significant landmark which is easy to defend and that is the stone bridge over the dry riverbed. All very thought out so far.
And there is the obvious giant plant in the room. The mid section of the stronghold looks as in the comments below already mentioned very much like a plant. Plants are not made forever and at least in the desert they tend to grow very slow. So if this is a plant one have to live in sonstant fear some of these "trunks" will break of. Also plants tend to burn very well (very old wood of some sorts does not I know). Also if there is a siege and all the people are in the upper part this plant conceals the enemy if attking from the ground very well. The plant itself is just huge and gives the stronghold a majestic and archaic look.
I hope you see my problem here I cannot imagine a kind of sci-fi warfare were this kind of sronghold brings a major advatage to the defenders (aside from giant creature carried warmachines that just ram into cities to conquer them).