A bunch of us explored some of the logging ROW's in the White Mountains last year. The after mentioned Sawyers River ROW is now a hiking trail and can be reached by either the former town of Livermore or on the other end along the Kangamangus (sp?) Highway. We hiked the whole way. Of course all the rails are gone, except we did find some rail with a frog still in its original location. After doing some research, we found that the rail laid for the Sawyer River was purchased from the Eastern RR, so we were looking at some real RR history.
We also hiked the Rocky Branch, which connected with the MEC at Glen. That ROW is mostly a hiking trail, so it is very accessable. If you bring either Belcher's or Gove's logging books with you, you can compare the old photos with what you are looking at and imagine where the buildings supporting that operation were located. We also found a long piece of rail still buried in the ground.
If you know what you are looking for you can still see a lot of it, even if many of them went out over 60 years ago. Some ROW were totally impassable, but you could still make out that they were a logging ROW. A lot of fun.