Saucon Rail Trail, from Living Memorial Park near the south terminus to Bingen Road just past Reading Drive parking, and back.
I wore a heart rate strap, so those readings should be better than usual.
Took narrow path through woods on the way back; I think it's a walking loop (gravel, slightly coarser than what's on the rail trail) but it didn't say no bicycles so I went. One dog-walker who had her dog under control (as did all the others I encountered, but I encountered mostly other bikers).
And a very large fungus growing by a large tree. Glen said he saw some of these at Green Lane too.