Having just missed a WAB train departing Lauterbrunnen the staff placed me on an empty second train following closely behind the first. You can see it leading through this tunnel somewhere along the route between Lauterbrunnen and Wengen. There are four tunnels between Lauterbrunnen and Wengen, the fouth lies just downgrade from Wengwald, and reverses a train's direction nearly 180 degrees. See this map.