The Tunnel is a location in Fear the Walking Dead: Passage.
It's entrance is located in the Construction Site and it runs under The Border between the U.S. an Mexico. It is, at first, implied that The Tunnel was/is being used for the purposes of illegal emigration and the smuggling of contraband. Both Gabi and Sierra believe it to be a way to cross to the (perceived) safety of Mexico. However, The Tunnel is booby-trapped and houses several Infected as well as several Boarder Patrol guards. It is revealed by Colton that The Tunnel in facts houses a bunker and that several members of the Boarder Patrol were going to use the bunker to hide out and escape the Infected.