My initial idea was for a downed 'cursed' submarine with the crew overtime becoming a cult to an eldritch horror, and anyone entering the wreckage is teleported away, along with the whole submarine, to a different part of the world, where the mystery of what happened onboard is revealed while a rescue team is sent out to try and locate the expedition team who have tracking beacons on them.
I guess there's a sort of mix of elements from Bioshock and Call of Cthulhu, as well as old Cold War conspiracies.