Mount Katahdin Deer Island

[Novelist]

Has anyone been trapped inside the mountain? Is there another way out?

[etwas]

nope. there's only the gate and u can only wait for someone else with a keycard to open it from outside. good luck! there's always the f11 option^^

[Longhaul]

You talking about the Bunker Vault? No.. there is no other way out. If you get locked in there im pretty sure the only way out is when someone else comes with the passcard to open the door again.

[String Eastwood]

To get out of the Katahdin Military Underground Complex (KMUC), there is 2 ways :

1 - One on the top across the maze (you have to find it but it's not to hard. Just try to reach to red corridors maze and it's not long after that.
When the corridor becomes veeeeery long with no crosspath, you have 50% chance to be in the right direction.
Why ? Cause there is 2 corridors long like this.
One is on the wrong side of the big ventilation you've seen when you passed the initial gate.
The other one is the good one, and you're coming back to the card room.

2 - The other way is at the bottom, 350m below, but you need to have an helicopter down there (mod only).
Logicaly, it's by the huge well that you may come with your heli and leave in the same way, not the other (read 1) to not let your heli down there.