Running, biking, skating, strolling, walking, frolicking, sprinting, slacking - all things that can be done on the Montour Trail. As Miriam W. mentioned, Arrowhead Trail is a subsection of Montour Trail and that's the area I most frequently use as well.
In the spring, summer, fall, and the mild winter months it's such a great place to get outside and get in some exercise. Depending on the season and time of day you decide to go, it can get fairly crowded. But it doesn't bother me too much b/c most people are courteous of others and give you your space.
But if you are fortunate enough to find a time of day when it's not so crowded, it's a great place to go and be quiet with your own thoughts in the outdoors.
I have seen some squirrels, deers, and wild turkeys roaming about. Kinda freaks me out when I'm by myself - not the squirrels so much as the deers and wild turkeys. I think they are so used to seeing humans they don't scare off very easily.