[1] Listed in ascending order of affordability.
As an example, I randomly picked a particular address on walkscore.com (https://walk.sc/37yZciv) which gets a walk score of 91 (walker's paradise), but that particular address is on a large 7-lane street with not a lot of walking infrastructure around. I'm guessing the score might mostly be driven by proximity to stores, which doesn't necessarily matter in this case. Better metrics may be such things as amount of car traffic, noise levels, size of sidewalks (in comparison with size of streets), amount of small streets and distance to larger roads, etc..
I wonder if a website exists that puts more emphasis on how nice it is to walk in a neighborhood vs. mere practicality?
Anything south of Oakland/SF is mostly strip mall hell, but parts of Alameda County, Contra Costa County, Marin County and San Francisco might be what you're looking for.