I’ve come across that tale in a couple of obscure travelogues from the 80s, but I can’t find any cartographic proof that such a valley exists. It’s more likely a clever narrative hook than a lost geography, though the way those games layer the lore suggests the designers were playing with the idea that “unexplored” is just “untamed” for players. Still, who knows—there might be a forgotten fungal hotspot somewhere that inspired the myth. The mystery keeps it interesting.