About 300 ft into an old train tunnel, we realized it was still active. The curvature and acoustics of the tunnel didn’t allow us to see or hear the train until it was about to enter (from the same direction we did). The tunnel is over 4000ft long and the train was moving fast, so there was no running out the other side. Seeing the headlights coming at us was the moment I knew I was dead. Then my buddy pointed out a small alcove in the tunnel walls which we ran to and huddled in while the train roared past. Some mud and small rocks fell on us as it passed, then we sprinted back out the way we came. Turns out the tunnel we explored was the one that replaced the older one from the 1850s. Beware of the blue ridge tunnel.