Olympus Mons
Olympus Mons, a shield volcano on Mars, is the largest volcano in the solar system. It is about 624 km wide and about 25 km high, which is 3 times as high as Mt. Everest. Olympus Mons has 6 calderas at its peak and is more than 1 million years old. Mars has had volcanic activity in the past but all the volcanoes are extinct now.
Theia Mons
Theia Mons is the largest volcano on Venus standing 800 km wide and 4 km high. Theia Mons stands at Beta Regio, a region on venus known as volcanic rise, and is extinct. Its caldera is in an oval shaped and is 75 km long and 50 km wide.
Moons With Volcanic Activity
Io
Io is a moon of Jupiter, that shows signs of volcanic eruptions. Sulfur volcanoes on Io create a magma umbrella or erupt like a fountain.
Triton
When Triton erupts, it is so cold that the nitrogen there freezes. The suns heat defrosts some of the frozen nitrogen beneath the surface. After that the nitrogen, now liquid expands and erupts through the surface.