What's inside the bunker in Sven Coop's Zombie Nights?

Every self respecting shooter has its own zombie survival mode, and for good reason. They're fun time wasters that require about as much brain power to make as they do to enjoy: Not a lot. Which is not an insult, they're dumb fun, it's just that they're dummy simple to make. So imagine my surprise when I came across a sven coop map with hard zombies, indepth survival mechanics, an actual end goal, and a mysterious blast door located in a secret bunker underground, that can allegedly be opened if the right conditions are met? Let's see if we have what it takes to open the door!