Having read it 20+ years ago in a very different language, I can offer only my own translation back to English: "Hellgate is not a place, it's a state of mind." Appears close to the end of the book, right before the main protagonist's attack on her arch enemy. The exact wording is probably very different but the message should be about right.
This is the quote you have in mind.
"Where is it?" The navigational systems were no help. "It's not marked! I can't find it anywhere."
"Where is it? Fool! Hell Gate is not a place—it's a condition."
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Yep, that's the one. I was not terribly wrong about the wording, in the end. – sigil Oct 17 at 22:33
