In 1958 Scientists built   a Mulitverse Machine Portal allows you to go into a different Universes.

(like show you and take you to in Video Games, cartoons Shows, tv shows and movies universes 

But they Shut it down and Realized is too Dangerous they Locked it away, seal it off and barricaded it. 

Now is Overgrown 

That's where the multiverse Portal in that Mountain.