Patrick and I walked across Boston, on Saturday. It was excellent! This was a follow-up for me to my walk across Philadelphia last winter. Boston's a smaller city; I'd estimate our total distance covered was about 14 miles, whereas Philadelphia was about 20. We started in the SW corner of incorporated Boston, in Hyde Park, and worked our way up through Mattapan, Dorchester, South Boston, downtown, then across the Zakim into Charlestown and finally out of the city, back into Cambridge. Strangely enough, there's no way of walking to East Boston (incorporated as part of the city of Boston) without leaving the city; there are only tunnels & ferries.
Walking through Mattapan and Dorchester was the kind of eye-opening, "I didn't even know this part of Boston existed" kind of experience I was aiming for. These two neighborhoods probably account for 40% of incorporated city area, and yet seem like they might as well not exist to the white / business / academic Boston. South Boston, on the other hand - supposed to be a really rough part of town - seemed pretty gentrified and unremarkable, to me.