楼梯

I saw him on the stairs.

He took the stairs/steps two or three at a time.

A big staircase winds up from the big hall.

top/bottom stair

stairs to the attic

staircase of thirteen steps

winding staircase

circular/corkscrew/spiral staircase

steep/narrow stairs

landing

banister

stair-window

come/walk/go down the stairs

fall off a staircase; fall down the stairs

ascend/descend the stairs/a staircase; go up/down the stairway

climb the stairs

a flight of stairs; a stairway/staircase