A stair that is made completely of winder treads with a very tight circular radius. Spiral stairs appear to corkscrew their way around a center post. Sprial stairs take up a very small footprint so they are popular where a stair is needed but cannot take up a lot of room (like in a loft). Click here to see a photo of a spiral stair.
A circular staircase -- the most economical, if not the most convenient to use, method of accessing upper floors in a vertical tower; also, easier to defend.
a space efficient, stylish and modern means of getting from one floor to another