So, that bunker on the beach next to the castle wall has a basement, with a weirdass door...
Ok, but that could just be something to throw us off track, or just a sealed off part of the map from earlier development before Raap cut some of the playable area. Except. Well, that door doesn't block the camera very well, and behind that door, is another door.
And behind THAT door, is another one.
So there's definitely something back there, the doors are probably hooked up to three separate triggers.... going by color, I'd guess, one near the Allied base, one near the Soviet base, one in between somewhere? The catch is finding them.
Also there's some kind of weird particle effect back there, looks like a portal of some kind? Couldn't get any kind of a good screenshot of it though, limited view and whatnot.