1. Activate each big sphere of swirling corporeal mana by using the core from the golem boss fight. Do this in triplicate: once at the Forest Ruins for Water, once at the Valley Ruins for Air and once at the Seaside Ruins for Fire.
2. If you have not already done so, make certain you reported all three of those accomplishments one by one to the Lord-Mayor at his manor in Initial.
3. If you missed the event in Valley Ruins which unlocks the map for Deserted Village, trigger it by visiting the northern tip of the Valley Ruins area Scenic Ridge.
4. Visit the Deserted Village and walk down the beach (Village Remains) to the cape (Monument Hill) and then up the cape to the cairn at its tip. Interact with it, after picking up the two Whispering Shards from the singing statues on the left and right side of the cape. This will trigger a plot event, all three Singing Shards glowing and vibrating, then a video cut scene, the aftermath of which dramatically changes the world map by raising the remainder of the continent of Avalon out of the ocean.
5. Return to town and go talk to the Lord-Mayor so that you may take credit for this. You will get some conversations pertaining to your chosen focal main character's plot thread with some brief conversational input from your party members related to their own storylines in juxtaposed relation to the focal one. It's about motives. Then you hear the fascinating flashback origin story of the Lord-Mayor first setting foot on Avalon Isle ten years ago when all it was is Monument Hill poking out of the sea all by itself. He prayed to the cairn and then the Isle of Avalon rose out of the sea where there had previously been just the ever so tiny island of what is now Monument Hill. From this point onward, the Boiling Sea is no longer a destination on the world map. (I really hope it had no exclusive map completion dialogue lore or modified stances to collect.) Great Crag and Shipgraveyard are now viable destinations and shop stock appears upgraded.