Due to me mistaking which bridges across the river can actually be accessed from the path that runs alongside of the Boston side of the river (you have to be on the other side of the expressway to get to some of them), I ended up taking Tim on a 7.4 mile walk
yesterday, from the Seaport District, along the Esplanade, and back to Central Square station. What I was actually hoping to do was walk along the Esplanade for a while, then cross into Cambridge to Kendall Square. But that bridge looked really long, and I saw another bridge up ahead on the map, so we kept going. And found that we couldn't get to that bridge. So, we kept going.
It was, at least, good to confirm that I could walk home from downtown if there were some sort of transportation outage.