Scuba dive through the Mariana Trench, but that shit's hollow

There's a tunnel at the base of it that goes straight through to the other side of the world. There's a gas station halfway, a couple of fast food places, and a holiday in. There's no feasible way they could make it, but you're in the tunnel. There's other people too; people that live on the wall of the ocean and people who drive through the tunnel to go to work everyday. What now?