Silverfish is a hiking trail around some beaver ponds in the Grater Road conservation area. Park at the Grater Road trailhead on the Amherst/Merrimack line. My brother and I put this on trails near our childhood home, hoping to bring more people to this area.
You are looking for a lock n lock, 60 feet off the trail on solid ground. It is near a beaver dam, but not in the marshy area to protect the beaver dam.
Congrats to TeamBedrock on the FTF!