Any more US walkables besides NYC and Boston?

Hmmm. Well, parts of Seattle are pretty walkable. Their light rail goes all the way to the airport, but you can hop off almost anywhere. The most popular stop is near Pike Street Market. We got off at a few other stops looking for specific eateries. Pike Street is very touristy, and a bit expensive, but the food is good.

I wouldn't advise Phoenix. Though there is a core area downtown with museums and restaurants. That area is very walkable. The Heard Museum is reputed to be the best Native American museum in the world (though I'm not sure how they determine that). It's probably the most unique museum you'll find. The art museum doesn't have any masters that I'm aware of, but it is nearby the Heard. Only walk it in the winter. If you're not acclimated, walking it in the summer can be deadly (heat).

I really think the most walkable cities are going to be back east. Out west, we sprawl. Long distances. Back east, they build up and compact. Better for walking.