From Dark and Darker Wiki
Description
A special extract that is currently only available in the Goblin Cave Map in 3 different locations. Extracting the dungeon from this point is only possible once the door is opened, so waiting for it to do so is necessary. To clarify, the door has only been observed to open after 5:00 minutes left and remain open for a limited period of time. Even when you are in the Death Swarm(Red Zone), there is a chance that the door will not open until the last second.
Should mention that only one player is allowed to use this extraction method. After being used once, rocks fall and collapse the exit, making further extraction via this method impossible for the rest of the match.