My usual mode of commuting is to walk to a station, take a train into Boston & then things get interesting. The biotech zone of Cambridge is not particularly near North Station, nor are there truly convenient transit connections.
There is a little blue bus sponsored by a consortium headed by MIT which starts at North Station & ends at my office. It's a good option, with a few caveats. First, Codon doesn't belong to the consortium (nor will they take us, we're too small), so it's $1 a ride. That adds up over a week. Second, the route maximizes coverage of employers over minimizing travel time, so other options can beat the bus, especially if you aren't in sync. Third, one needs options when the bus is running late or has just been missed.
For the part of Cambridge I'm now based in, any reasonable option is centered around the Red Line, but will also involve a bit of walking. Since the streets are in a pretty ordered grid in Cambridgeport, and we're a few blocks in each dimension from the subway station, there are a variety of reasonable routes.
The big advantage to walking is that you see things you would miss at the speed of a car or even the bus. Everything is closer & you have more time. I like spotting dogs & cats and looking at the details of gardens. There is one crazily cut & painted fence which I pass routinely, whose various designs & inscriptions could keep me interested for months.
Today I stumbled into an ethical dilemma: is it okay to taste the raspberries when someone's canes are sprawled through the fence & onto the public sidewalk? I resisted, but not by much. It was also a big surprise to find that Altus has a peach tree in their parking lot, which is laden with peaches. There's also a few grape arbors around, so if you know the right way to walk this time of year one can find the wonderful aroma of overripe Concords.
By far the biggest pleasant surprise I've ever had in the neighborhood happened a year or so into my Millennium career. I was walking from Fort Washington (a building now entirely occupied by Vertex, which at the time subleased it to MLNM), in a foul mood from the meeting which had just ended. I was pretty much staring at the sidewalk directly in front of my feet when a jarring thought came from my peripheral vision. Did I really just see a chicken? Sure enough, the little garden had 2 or 3 beautiful poultry strutting & scratching. I saw them there off-and-on for several years, but I haven't seen them for a long while so I assume they're gone. I really do miss the Cambridge Chickens.