I exit the Red Line via the building that houses Vinalia (technically the address is 101 Arch Street). So every morning I am greeted by the smell of freshly baked muffins (and sometimes roast turkey) coming from the Grassroots Cafe. The past couple of weeks I've stopped in to purchase a morning treat and I am always pleased. I've had the bran muffin and the cranberry muffin ($2 each) and they are delicious, huge and satisfying. The people working there are very friendly. The only problem I have is that the muffins aren't labeled in any way and they are still in the baking tin, so if you can't identify a muffin or have an allergy you'd better ask. I found some additional info on Yelp since I've only tried their muffins: Their coffee is good and doesn't come with a mile long line like Dunkin' or a second mortgage like Starbucks. They make their own fruit cups. Also, they assemble their own prepackaged salads. Nothing looks like it came out of a machine. They bake their own muffins and croissants. They roast their own turkey as well. All that being said they have a smallish menu of soups, salads, and sandwiches.
You can see the cafe windows from Summer Street.