The Great Meadow is neither great, nor a meadow. It is, however, a pretty good place for some smooth singletracking right off of the Minuteman bikeway.
You can get here from downtown Boston using bike trails. Really.
Okay, so I'm getting a little obsessed with finding "wilderness pathways" in the Boston suburbs. Maybe it's my mortal fear of road biking around Boston drivers, but my quest to find bike paths linking different parts of the suburbs brings me way too much enjoyment.