Chapter 1 says:
Is the enigma ever resolved? I've been searching through the other chapters, particularly 10, 12, & 13, but haven't found anything.
On the south of the island, though, a temple survives fairly intact, preserved by layers and layers of ritual magic. The huge compound, an eerily empty marvel of Stone Age architecture, must remain for now an enigma. The designs on the walls come from before the invention of written language, so while clearly this place was very important at one time, its intended purpose and its original creators are inscrutable.