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human
[Star Wars Empire Strikes Back] Why was that cave on Dagobah strong with the Dark Side?

When Yoda tells Luke to enter that "Dark Side" cave and fight the vision of Darth Vader, what exactly makes this cave strong with the dark? Is it just that its appearance resonates with fear and anger?
gpt
Canon: There's a vergence in the Force there,  infested with the Dark Side. It's origin is unknown.

Legends: Centuries ago a powerful leader of a group of Dark Jedi was killed there, and his death caused an intense dark presence to linger there. Similar phenomena have been seen in locations where other Dark Side users were killed.