I found a dark tunnel after finishing an exploration mission containing invisible enemies. After sneaking through/ speeding through on my sparrow :D I found more invincible enemies and pretty much died instantly, has anyone else found anything like this ??????
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Most people have found that, since if you have a sense of exploration, you'll surely encounter that amongst your travels. Overall, it's not much of a secret anyways. FYI, They aren't invincible, I've killed one before, it just takes determination, and a whole lot of rinse and repeat.