The degree to which something is steep, or goes up or down quickly.
Steepnesses can make things hard to climb or go down.
Examples:
The steepnesses of the mountain made it hard to climb.
She didn't like the steepnesses of the hill.
The steepnesses of the stairs made her tired.
The steepnesses of the rollercoaster made her scream.
The steepnesses of the valley were scary.
The steepnesses of the slope made it fun to slide down.