This gotta be a giant dome! The Mars Reconnaissance Orbiter (MRO) took this image with a range of 296.5 km (185.3 miles) to the target
But as usual you decide what you see.
Please watch the video, hit pause to study the area around the dome also.
Visit his site at: http://whatsupinthesky.com
Original NASA link: http://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA17985