User blog comment:Darkcloud1111/Good Idea, Bad Idea~Mountain Glenn/@comment-5217560-20141013022054/@comment-3146930-20141013035102

What I mean is according to Oobleck, Vale sealed off the tunnels only after they had accidentally opened up a cavern that allowed subterranean Grimm to enter and finally destroy the city. However that fact that there were tunnels leading from Vale to Mountain Glenn means that people didn't have to risk running into Grimm in the forests because they had subways lines they could have used to evacuate. Even without the trains, the tunnels would have been enough. I understand why the caves were sealed, but not why the people simply didn't leave the city being constantly attacked by Grimm; even if it was Vale's first serious attempt at expansion (according to Oobleck).