The best compliment you can give the Skyline Trail
at the Fells is that you almost forget you're always comfortably nestled within the Boston suburbs and often parallel to some of the worst rush hour traffic New England has to offer.
Really though. Despite all the nearby hullabaloo (or perhaps somewhat because of it) the relative vastness and peacefulness of the Fells are endlessly remarkable. The continuous seven some-odd miles of mixed singletrack and doubletrack cross plenty of other trails, dart up and down countless rugged rocky outcrops, and wind into and out of typically suburban neighborhoods, and you'll likely see a greater variety of terrain than anywhere else in the state and possibly even anywhere else in New England.
Parking is available all around the Fells, but the easiest access is probably from the Sheepfold Lot. This lot and area in general can be crazy on weekends and in the after-work hours. Off-hours are best in the Fells for avoiding the very same sense of craziness you came to escape in the first place.
Even in ideal conditions, keep a good head about you if you want to remain on the white Skyline Trail
proper, though it's generally easy to connect back to the trail or to follow the parallel orange Reservoir Trail or green Mountain Bike Loop
if you get off course. Less-than-ideal conditions often make the trail more fun as they amplify the transient feelings of remoteness than can make the Fells so special.
One of the main highlights is Wright's Tower at the southeast corner. This outcrop, to me, embodies the Skyline Trail
as a whole: you can at once see the Boston skyline and the dizzying traffic on I-93 below, and yet somehow feel like you're on top of a much larger, more remote hill.
Deer, turkeys, etc.