Ancient's Bone Graves can be found in the northern area of the Valley of the Void. Collect Ancient's Bones. Afterwards, speak with Theletar Hephon at the Halo of Helion. Use your quest tracker to see your progress.
Theletar Hephon: Try setting that shell on fire - it will crack in half. Theletar Hephon: I make prophecies based on the way it gets split. NakanoAzusa: Is that the secret behind your predictions? HiiragiKagami: Sounds bogus to me! Did something happen? Theletar Hephon: Yes. The Spirit Control Machines happened. NakanoAzusa: What of them? Theletar Hephon: I'd love to find out who installed these Theletar Hephon: contraptions. Who would do that? And more Theletar Hephon: importantly: why? NakanoAzusa: How can we find out? Theletar Hephon: I'm trying to burn bones to complete my Theletar Hephon: incantation. However, regular firewood doesn't work. HiiragiKagami: He's burning bones?! Theletar Hephon: Can you find bone heaps for me, young Aitan? Theletar Hephon: They're all around North Amarkand. I'll need the Theletar Hephon: clean ones - they're called "Ancient's Bones." Can Theletar Hephon: you bring back ten?
Reminder Dialog
Theletar Hephon: Head towards the center of the Valley of the Void.