Short sci fi story - endless stairs

About this time last year, I read this short story online, about a man (in a department store?) who finds a flight of stairs where he didn't think one existed. He goes down them to see what's below, only to find a landing with another set of stairs, and another, and another, ad infinitum. The story ends with him still going down the stairs, thirsty, and possibly near death, knowing that he can't walk back up at this point, and they will probably never end. Sounds cheery, doesn't it? But it really was great. I believe it was nominated for an award, or its author was a classic sci-fi bigwig who recently died, or something like that - there was a reason it was available freely online and came to my attention. An award, I think. Anyway, I'd like to track down more things by this author. Any help would be greatly appreciated!

Also could have been in a subway. One of the two. Thanks!

I am quite certain I read this in a sci-fi anthology when I was in college, which would have been before 1976.

I believe you're thinking of the story "Descending" by Thomas M. Disch; however, Disch's story has descending escalators, not stairs - making it even harder to go back up.

You're absolutely right. I'd forgotten they were escalators. Now I remember - there was a part where the narrator tried to climb back up the escalators the wrong way. Thanks!