This trail runs just under 20 miles along the Perkiomen Creek in southeastern Pennsylvania. The trail mostly follows the former route of the Perkiomen Line of the Reading Railroad. As a rail trail along a waterway it is mostly flat (excepting one short section) with several paved sections. There are numerous access points and comfort stations along the trail. The southern end connects to the Schuylkill River Trail near Valley Forge National Park.
For more information see the Montgomery County website.
You can find a video of one of my rides on the southern portion of this trail on Mark's Bike Tock on YouTube.
Here is the elevation profile: