There is light at the end of the tunnel.

In a long rail tunnel the first sign is not visual.

The sound changes. The pressure alters, the noise loosens, your ears do something — and all of it happens well before there is anything at all to see through the window.

Tunnels are hard mainly because the length is unknown from inside. Nobody can tell you how long, and anyone who claims to is guessing.

But there is a difference between a tunnel and a room, and it is the only difference that matters here. A tunnel is a thing you are moving through. Even where the walls look identical, the position is not the one you were in an hour ago.