The Valles Marineris hemisphere of Mars

This is a split in the Martian crust 4000 kilometres long (about a fifth of the distance around the whole of Mars), up to 600 kilometres wide and seven kilometres deep. The Grand Canyon is a mere 450 kilometres long, up to 29 kilometres wide and 1.6 kilometres deep.  
 

	Size comparison between Earth and Mars

Then there is the Hellas Basin in the southern hemisphere, which is an enormous impact crater 2300 kilometres in diameter and more than nine kilometres deep.

But perhaps most striking of all is the general difference in height and surface roughness between the northern and southern hemispheres. The northern hemisphere is smooth and flat and on average six kilometres lower than the rugged highlands of the south.
 
 

	Olympus Mons, 25 kilometres high, is the highest volcano in the Solar System

It has the highest volcano in the solar system, Olympus Mons which stands at 26 kilometres above the surrounding plain: Mount Everest is only one third as high.

Olympus Mons lies at the western edge of another gargantuan feature, the Tharsis dome which is a 10 kilometre-high, 4000 kilometre-wide bulge in the Martian surface.