Abandoned alien outpost.

Environment concept exercise...
Exploration of abandoned alien outpost. The megastructure has a diameter of 3 miles and is located on the moon XJ162 in the solar system Kepler-186. On the mother planet, signs of similar but many times larger megastructures have been found which were almost completely destroyed by erosion. Since the moon XJ162 has no atmosphere, this structure is completely preserved. The age of the structures is estimated to be 20-30 million Earth years old. The reason of the structure's use is unknown.