About where they are, it's an oceanic cave. There's not a lot vegetationwise to go with, but plenty of
A few days ago, one of them found a lagoon with palm trees, so tropical or somewhat warm. There's a banana plant in the cave that supports that. But, a fallout shelter and sewer which suggests inhabited and developed and engaged in the Cold War?
I'd say the Pacific like the Marshall Islands or I don't actually know how the Caribbean prepared for the cold war. Maybe Cuba? Assuming earth, but everything else scenariowise has been what seems like earth. But they could just have built approximations of earth cities in the right historical period.