Reef, Dreadnaught, and maybe Meridian Bay.
I'm not sure about the Ishtar Sink or the Hellmouth yet.
English
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There are audio files referencing a return to the Hellmouth, but I don't remember hearing anything specifically about the Ishtar Sink. That said, it would be a bit weird to revisit every area from D1 EXCEPT for there.
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It seems my dream is coming true if we do return to Venus...