Because there is no Hyperspace portal there, I think the dialog from Florin when talking about the Book of the Dead mentions where the entrance is, similar to how, once my name is in the book and I talk to Florin again about the book, my character answers hinting where to find the next place to go.
I felt silly once I realized the entrance was on the south east of Perdition Harbor, however I had to find https://github.com/flareteam/flare-game/wiki/World-Layout on a search engine to find it.
Because there is no Hyperspace portal there, I think the dialog from Florin when talking about the Book of the Dead mentions where the entrance is, similar to how, once my name is in the book and I talk to Florin again about the book, my character answers hinting where to find the next place to go.