The Tunnel is how Coloradoans refer to the Eisenhower Tunnel, the highest vehicular tunnel in the world. It carries I-70 through the Continental Divide and through to the killer powder on the other side.
Usually used when talking about how long it's going to be until you shred the gnar.
"How long til we get to Vail, man? I can't wait to rip with my new board."
"At least an hour, we're not even to The Tunnel yet. Better light that blunt now."