Divine Disappearance
After Vaan put together Astoria's information, he figured out everything regarding Pangea and the moon megastructure.
Although there was also a chance that Astoria's information was inaccurate and made up, the puzzle pieces fit so well that he chose to believe it until proven wrong rather than deny its possibility.
After all, he had seen the Pangea continent from outer space – it indeed had some faint resemblance to a resting dragon.
The world of Pangea was a cage used to trap the Ancestral Golden Dragon Pangea, and the moon was a megastructure her enemies had built to monitor and enforce her captivity.
That was what Vaan had found inside the center of the moon.
It was the ruins of a large colony filled with mechanically-constructed buildings and devices that had been destroyed or damaged beyond recognition. Reparations were impossible, let alone restoring any functionality it had to understand its history and purpose.