Well, I've been noticing those cliffs you sometimes encounter while exploring. You can't get over them, but you have to go around. I think it would be a unique idea to be able to craft stairs on them to reach the top part of it. If you don't know what hills they are, they are the hills which a cave can be formed in.
They can be destroyed, but faster with a pickaxe.

Those are the cliffs. Ignore the cave there.
Anyone agree on the idea?
I know it has been suggested, but I really think this needs to be added.