Park in the parking lot by the boat launch in the Veterans' Park on Water Street and walk to the trail beside the gazebo. This area is a very pretty spot by the river and open to the public year round. The Penquis Valley Middle School has made a nature trail as part of a community service project. Cache is near the trail and should be accessible year round, but you will need boots or snowshoes if the snow is deep.
Parking coordinates are N45.15.127 and W 68.59.312.
Congratulations to 21alpine on being the first to find!