This cache is along the Farmington Canal Heritage Trail also called East Coast Greenway.
There is a kiosk at the parking area and signs along the trail with the history of this area.
There are signs along the way that will explain the gun shots you hear.
The cache is 2 bottle caps under small rocks
You will see 2 metal fences on either side of trail. You go past either one and you may soon see the tunnel!!!
On the tunnel walls were numbers that would take you to the second stage of the cache that was near here across a small bridge that has washed away.
The tunnel was built for the railroad.
Thanks to lawflowers for posting a picture of the tunnel.