A stairwell is the vertical shaft or enclosed space that contains a staircase in a building. When you look up or down while climbing stairs in an apartment building or school, you're looking into the stairwell: that tall, narrow space that extends from floor to floor.

Stairwells serve an important safety function. During a fire, elevators stop working, but stairwells provide a protected route for people to escape. That's why stairwells in large buildings have fire-resistant walls and doors that close automatically. In an emergency drill at school, everyone uses the stairwells to exit safely.

The word describes the architectural space itself, not just the stairs. You might hear an echo in a stairwell because sound bounces off the walls in that enclosed vertical tunnel. A ball dropped in a stairwell might bounce down multiple flights before finally stopping. Some buildings have grand, open stairwells with decorative railings you can see from the lobby, while others have plain, utilitarian stairwells tucked away behind heavy doors.