Series of steps

STAIR

Think of what you climb to reach a higher floor one level at a time.

"Series of steps" directly hints at a physical set of steps you climb, which is a stair. The word "series" reinforces the idea of multiple steps linked together, making stair (or stairs) the natural fit. It’s a straightforward definition with no hidden wordplay—just a common term for what you’d find in a building or on a staircase.