If a structure was really built on Mercury, it would have to be incredibly hardy.
Temperatures can swing by up to 600C as night turns into day — such is the raw power of the nearby Sun to what is its closest planet. There is no atmosphere to mitigate or distribute this heat, resulting in days of up to 430C and nights as low as -170C.
Needless to say, the opportunity for a picnic at a nearby scenic crater would be very limited.
Once again the evidence of extraterrestrial structures involves massive blow-ups of small and blurry satellite photographs that have been processed into an interactive map of the planet’s surface.
However, you can clearly see the face circled!