I suggest that "The Grand Expanse" is Atlantis, and Atlantis is the ocean/sea that splits us between Fluorite, remember "One side left to memory and lost beneath the waves"
Fluorite may be the "Memory" and "Lost beneath the waves" may be temple of dreams, and over the years since we left our original homeland to seek out the current "Feral Lands" Temple Of Dreams collapsed and fell into the sea. Eventually one day, ruins of the temple drift somewhere warmer in the sea. "Old stone feels warm again"
this is getting soO interesting..