I don't have trouble with stairs. I suppose this is good as both the house I grew up in and the house I live in now have lots of stairs. Most houses here do, it's just how they're built.
I don't think I could go up stairs on all fours if I tried - but then, that makes me imagine how unnatural it must feel for people whose instinct is to do that to do it on their feet instead!
I generally don't mind elevators either. I try not to take them as I figure I need all the exercise I can get, but I do sometimes, especially if I would have to climb 10+ flights. That said, I am definitely not fond of really packed elevators because of the close proximity to many people; but I can deal with it. When I was younger I used to worry the doors would close on me; now I don't think about it much. (Modern elevator doors are supposed to stop closing if something is obstructing them, of course. I always knew that, but used to worry about a malfunction.)
Then there are escalators, which I used to hate when I was younger. Being rather uncoordinated (though apparently much less so than many other people with AS) it took a lot of practice for me to be good at getting on and off them, and it is still something that requires concentration for me. (I am not sure if most people have to really concentrate on this or not; perhaps everyone does.) Nevertheless, I can now manage them well enough, and the same goes for moving walkways (e.g. at airports).