>>57967999I don't recall ever reading or hearing anything like that, OP, and I can tell you there were all sorts of wild and crazy rumors and "secrets" back in the heyday of Gen 1.
What would've been crazy cool, imo, is if the Cerulean Cave would've essentially been what you're describing, only y'know, accessible still. Keep it post game, make it in a very isolated, hard to reach area that requires a lot of traversing and HM moves to overcome, build it up with some lore about how dangerous it is, perhaps linking it to some past secret government and/or illegal activities or experiments, or something. And obviously it would need a different name since it wouldn't be in Cerulean any longer.
