This is a high-resolution picture of the caldera of Arsia Mons, one of the largest volcanos on Mars and in the solar system in terms of volume and challenged only by neighboring Olympus Mons (the tallest at 27 km above the surface plain). The greenish photo below is a 3D-ready image of a section of the volcano. If you have the right stereo specs like the one sometimes used in select 3D movies in theaters, you may also view this picture in depth, so to speak.
It was taken in 2004 by the Mars Express spacecraft using its High Resolution Stereo Camera (HRSC). The other picture below it shows Arsia Mons in relation to Olympus Mons. See how they compare visually in terms of size. Note that Arsia Mons does not have a defined extremity, but it's established diameter is at most 450 km. Olympus Mons, which has a more defined area, is 550 km wide. Still, Arsia Mons is recognized to have the largest caldera known at 120 km wide. Mauna Loa, the largest volcano on Earth, would fit snugly on top like a bottle cap.