The light at the end of the tunnel is indeed an oncoming train! In this case, it’s No. 463 entering Rock Tunnel.

Cumbres and Toltec Scenic Railroad (Denver and Rio Grande Western) No. 463 is a 3-foot narrow-gauge class "K-27" 2-8-2 "Mikado" type steam railway locomotive built for the Denver and Rio Grande Railroad (D&RG) by the Baldwin Locomotive Works in 1903.