down the stairs.
to or on a lower floor.
pertaining to or situated on a lower floor, esp. the ground floor.
1. (used with a sing. v.)
the lower floor or floors of a building: The downstairs is being painted.
the stairway designated for use by people descending: Don't try to go up the downstairs.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.