Thanks gents for the fine tuning tips. I found a pretty good map of the area on the Isabella Stewart site which does go all the way up to I90 and Fenway. However, I noticed that the Beer Factory really is just an eating spot and not a microbewpub. The Sam Adams Brewery is somewhere along Brookline, but is it near Fenway? (I also thought Sam Adams actually brewed its beer off site in upstate New York under contract?) Are there any true brewpubs or microbreweries in the city that are convenient to get to?

The Blue line appears to the best option, since the shuttles are free to the station and I can get one of those Charlie cards/day passes.

Hopefully this fine weather will hold up for a few more weeks and I can do this day trip in January. NYC's my first such trip, using a neat AC pass that gives me unlimited travel within NAmerica for C$400 a month for two months, albeit just on Tuesdays and Saturdays. My plan is to do similar day trips to US cities I've not been to for a while, and that have an AC sked that can get me in before noon, and back out by 9p, and to cities that have good public transit between the airport and city centre.