Thanks.

The tunnel was dark with much cooler temperature. I estimate at least 5 or 6 degrees C cooler than outside under the sun. There were some wet spots on the ground from the condensation that built up on the ceiling in the tunnel. We didn't run into any animals dwelling in the tunnel. It was a short tunnel, probably only 100m long or so. There wasn't really anything cool in the tunnel, except probably the temperature haha.

There was some wooden tunnel cribbing on the other side of the tunnel. According to the info sign, the cribbing was destroyed when the railway was abandoned, but it was rebuilt during a reconstruction project.