What would you think this is if I didn't give a hint of it in the Subject?
What it really is, is much more phenomenal. These are vertical cliffs on Mars, today's
Astronomy pic of the Day. But what's really amazing is the size; there's nothing to offer perspective here, but these cliffs may be as high as 2 kilometers high!
The Apod says that there is a canyon that's almost twice that deep on Earth,
Colca Canyon in Peru. (Which hasn't made the
field of 64, World Landmarks - maybe because it's hard to get to see?)