Mountains are large steep hills found all over the world, but even ones in hot countries have cold climates at their highest altitudes. The tops of the highest mountains are dangerous environments for a human. The temperature is bitterly cold and there is very little oxygen in the air. The adjective 'montane' is used to describe mountainous areas and things associated with them. The highest known mountain in the Solar System is on the planet Mars? It is over twice the height of Mount Everest.