The Boston Harborwalk
This is something new to me. It is a walking tour of the Boston waterfront. It isn't complete yet, but it is a great idea. It goes from Deer Island in the North to the Kennedy Library in the south. There is a downloadable Audio Guide of the central Boston part of the walk. The website identifies all of the sites along this route. Clearly a multi-day activity (as in it would take a week to do it if you traveled the entire distance).