User blog comment:Darkcloud1111/Good Idea, Bad Idea~Mountain Glenn/@comment-5217560-20141013022054/@comment-3146930-20141013024221

The way Oobleck made it sound, they main city was on the upper level and they were using the tunnels for subway transport. However because of the Grimm attacks, evacuation was necessary but the subways were sealed off to prevent Grimm from using them to enter the city. So instead of Vale sending in numerous airships and Hunters to fend off Grimm for the evacuation, instead the people built an entire underground city without any kind of Grimm interference. It just doesn't seem to click in my mind how that was the better option in comparison to trying to leave the city. Not to mention if the Grimm either didn't know about or decided not to invade this underground city, why were the tunnels leading to Vale sealed at all. If anything they would have been the safer option.