For running, perhaps the Riverway?
http://www.yelp.com/biz/the-riverway-bostonLongwood is not bad, but is nearish to some run down areas, so ask the locals (who work at Longwood) about when/where to go. I think days should be fine. The whole area is pretty built up, with restaurants and such, and there is also a T (subway) stop at Longwood. (And the Green Line T can be pretty busy at rush hour, a word to the wise.)