Olympus Mons on Mars. Artwork of Olympus Mons (darker area, upper centre), as seen from the north. It is found on Mars, the fourth planet from the Sun. It is the largest known volcano in the Solar System. Its summit rises 27 kilometers (km) above the surrounding plains (Mount Everest is 8.8 km high), and the base measures 600 km across. In front of the volcano is a region of ridges and hills known as the Lycus Sulci (rough area, centre).