The structure is located on the Syrtis Major Planum area and is part of a large area of strange patterns, geometric objects and other curiosities that look for all the world like tubes and tunnels.
According to Star City - A Second Cydonia?, the structures most likely have a natural origin: "Large domes and tubes, volcanic in origin, cover the landscape, and several of the domes have partially collapsed, creating interesting structures. In many cases the uncollapsed parts are probably partially hollow and may provide a shelter from the extreme Martian environment."
Indeed, just because a feature looks artificial doesn't mean that it is. We are only beginning to understand Mars' climate, geology and processes. It is still hotly debated whether or not Mars ever had flowing water - and perhaps still does. Yet there are some features of this strange planet that are truly mystifying....
