Somerville has the happy chance to be sandwiched between two great little rivers: the Charles to the south of us and the Mystic which meanders along to the north. Since it's a much shorter walk to the Mystic now, we've been taking a bit of time to both enjoy the nature and revel in the relative quiet around us.
Though rather unimpressive-seeming at first (it is in heavy urban/industrial area and there is a bit of trash strewn about in some places), we've found that it's best to wander around with a camera, or at least a camera-eye. That's when you really start to open up to the beauty of the area, which consists of wetlands, woodlands and almost prairie-like patches. Interestingly enough, the part of the walk that cuts closest to I-93 (with cars whizzing by about 10' from us) is the part where we find the largest variety of flowers, birds and trees.
I don't know that I'd walk the Mystic reservation alone like I have done the with the Charles, but I think that I do enjoy it more right now. It has a wildness about it that appeals to me and I'm always discovering something new on my walks there.