A related question got me thinking - it it possible for a tourist to visit the service tunnel of the Channel Tunnel? It would be cool to visit the midpoint between UK and France.
There have been special exceptions, such as cyclists for promotional purposes, Top Gear Magazine driving it in an electric car, and behind the scenes tours for journalists. If your train happens to be involved in a fire or breakdown (more details on this incident), you could find yourself there, as the service tunnel exists for evacuation purposes.
There have been occasional rare opportunities for members of the public to visit, such as a 2013 tour for European Heritage Days; a video described that as the "first time Eurotunnel has opened its doors to visitors," and there doesn't seem to have been another such event since.
7It shouldn't need saying but... DO NOT START A FIRE ON THE TRAIN. :p Apr 9, 2018 at 9:42
4@theotherone Perhaps the most important advice ever posted on travel.stackexchange. On passenger trains, I think there's a good chance they'd try to contain the fire and drive on to get out of the tunnel, so you'd find yourself charged with arson and never even see the service tunnel. Apr 9, 2018 at 10:04
So @ZachLipton what I'm hearing is that it would need to be a really big uncontrollable fire ... ? ;) Asking for a friend.– brhansApr 9, 2018 at 15:25