I found these wonderful videos recently. Japanese railfans have the advantage of being able to shoot videos through the front windows of trains in Japan. YouTuber iso8 was invited by Swiss Federal Railways to shoot from the cab of a train through the Gotthard tunnel. These videos were the result.
The Gotthard Tunnel. Airolo-Goschenen
Note the spacing of trains in the opposite direction. This is a very busy railroad.
Part 3: Goschenen-Arth Goldau
Beautiful scenery and mountain railroad that climbs downgrade with loops and tunnels. You can also see the work for the approaches for the Gotthard Base tunnel. Even if the new tunnel itself is open, the amount of track realignment projects and improvements to existing facilities are a massive project all by themselves.