Olympus mons

Olympus mon is the largest mountain on Mars

At the height of 25km on mars is the largest volcano in the solar system and is nearly 3 times as tall as mount Everest.

It is thought that one of the reasons that Olympus Mons and the other volcanoes on Mars are large is that the Red Planet's crust doesn't move like the Earth's. This lack of active plate tectonics means that rising magma erupted on the same part of the planet's crust and slowly built up a very large volcano.

Eruptions of Olympus Mons and the other volcanoes on Mars are thought to have ceased due to the cooling of Mars's core.