It is only closed if the place has not loaded as a Darkness Zone. If it has the door is open. If not, then you can leave and come back in.
The only part you can't solo is the gatekeepers.
English
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The Gorgons maze becomes a Darkness zone once 3 people are or have been in the maze
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I have had the checkpoint before and gone through it solo so I could get people for Gatekeepers rather than some littles shits who would take the exotic chest and leave. I definitely does open for a singular person.
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I've tried it many times and it does not open
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Unlucky then? I always just load it up and go through the maze without a problem.