True, passing through a tunnel at 300 km/h was interesting when I traveled from Madrid back to Valencia. Basically you feel the air pressure drop in the train.

True, passing through a tunnel at 300 km/h was interesting when I traveled from Madrid back to Valencia. Basically you feel the air pressure drop in the train. They seem short but when you are inside a tunnel for 30 seconds at that speed, you've traveled 2.5km. And there quite a few tunnels along the way. It's what makes high speed rail hard. You can't have steep turns or gradients. So most hills/mountains have to be either tunneled or designed around; valley need to be bridged, etc.