Another comment mentioned the Philippines as the manifest frontier. SF is not on the same plane of reality in terms of density or narrow streets as PH, I would argue in comparison it does not have both.

This is the craziest I've seen, but it was 10 months ago which is ~10 years in AI years

https://www.youtube.com/watch?v=3DWz1TD-VZg

On that specific count, not really. There's a skate park north end of the Mission, and Stevenson St is a two way road that borders it, but it's narrow enough that you need to drive up on the curb to get two vehicles side by side on the street. Waymo's can't handle that on a regular basis. Being San Francisco and not London, you can just skip that road, but if you find yourself in a Waymo on that street and are unlucky to have other traffic on it, the Waymo will just have to back up the entire street. Hope there's no one behind you as well as in front of you!

Anyway, we'll see how the London rollout goes, but I get the impression London's got a lot more of those kinds of roads.

Any small city in Italy is going to be 10X more challenging than Boston

Various European cities come to mind: Narrow streets are something of a trope in certain movies/genres.

Not grandparent but I was rather thinking of medieval city centers in Italy or Spain.

edit: Case in point:

https://maps.app.goo.gl/xxYQWHrzSMES8HPL8

This is an alley in Coimbra, Portugal. A couple years ago I stayed at a hotel in this very street and took a cab from the train station. The driver could have stopped in the praça below and told me to walk 15m up. Instead the guy went all the way up then curved through 5-10 alleys like that to drop me off right right in front of my place. At a significant speed as well. It was one of the craziest car rides I've ever experienced.