Some areas of San Francisco are so steep that the sidewalk literally is a stairway; other times it’s just more interesting to have a stairway between streets… or a slide. I once saw a grown man with a briefcase matter-of-factly go down this slide and continue on his way down the hill. Why not?
#1 in the city for old book smell and creaky wooden floors. Too small to find anything specific you’re looking for, good enough that you’ll find something else instead.