Olympus Mons - Latin, "Mount Olympus" - is the tallest known volcano and mountain in our solar system. It is located on the planet Mars.
The central edifice stands 27 kilometres (around 16.7 miles/approx. 88,580 ft) high above the mean surface level of Mars this is about three times the elevation of Mount Everest above sea level and 2.6 times the height of Mauna Kea above its base. It is 550 km (342 miles) in width, flanked by steep cliffs.
It is possible that volcanoes of such magnitude were able to form on Mars because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years.
The top of Olympus Mons is above the Martian atmosphere, which means if you stood on top of this mountain, you would be standing in outer space.