Stairwell (noun)

1. A vertical shaft in a building in which a staircase is located.
2. The space or opening in a building through which a staircase passes.

Origin:

A combination of "stair" and "well".

Examples:

1. She leaned over the railing of the stairwell to look down.
2. The stairwell was dimly lit by a single lightbulb.
3. The fire escape was located in the stairwell.
4. He shouted down the stairwell to see if anyone was there.
5. The stairwell was the only way to access the roof.