Those weirdly shaped blocks are kinda sentient. Touching them will animate them briefly, and you'll hear wispers from the past.
Old stories long forgotten, testimonies from a long time ago are told trough them. Crafters of those stelaes are long time gone, but some of their tales still live in the stone.
Hidden in the ruined halls of the ancient dwellers, behind strong doors, it's their legacy to the new dwellers from this age. Like you, they didn't see the light of the sun in a long time.