The opening
The characters meet in a harbor tavern on Santorini while a storm shuts down the ferries. A salvage captain shows them a bronze cup pulled from a fishing net that morning. It is warm, perfectly dry, and stamped with a map of an island that should have vanished thousands of years ago. She offers them a berth on a dive the moment the weather clears.
The dive begins as a search for a wreck. Below the storm line they find a road instead, lit by coral lamps and busy with people who breathe the water. Atlantis is alive. Its citizens welcome the party cautiously, then grow frightened when they notice holy symbols, prayers, or any sign of faith brought from the surface.
What the party is trying to do
Follow the impossible road into Atlantis, find the source of the metal reaching the surface, and return before the storm closes the dive route.
A route through the campaign
- Dive through a trench where statues turn their heads toward whichever character last spoke a prayer.
- Enter Atlantis as guests and notice that every temple has one name carved over all the others: Poseidon.
- Search an Athenian embassy sealed inside a bubble of ancient air and recover the king's order abandoning Poseidon for the gods of Egypt.
- Learn that the party's beliefs are weakening the boundary around the city while priests prepare to confine them permanently.
- Reach the tidal palace as the sea itself takes human shape and Poseidon demands that the intruders kneel or drown.
Possible endings
- Defeat Poseidon and bind the city's survival to its people instead of a god.
- Renew the covenant and accept the cost of sealing Atlantis away again.
- Open a permanent route to the surface and lead the city through the upheaval that follows.
History and invention
Plato describes Atlantis as a powerful island associated with Poseidon. In his account, it attacks ancient Athens and is later destroyed by earthquakes and floods. This adventure deliberately changes that ending. The change of religion in Athens, Poseidon's rescue, and the surviving underwater civilization are part of the game story.
Content notes: religious coercion, drowning imagery, authoritarian rule.
Saving Atlantis Beneath the Tide for our next campaign.
That Mythic Mediterranean backdrop is doing real work here. It does not feel pasted onto a generic dungeon.
I would keep the real history notes for after each Atlantis Beneath the Tide session. My players love checking what was true once the spoilers no longer matter.
The job in Atlantis Beneath the Tide is to follow the impossible road into atlantis, find the source of the metal reaching the surface, and return before the storm closes the dive route. There is a nasty moral problem inside that objective.
Session zero for Atlantis Beneath the Tide: ask everyone what their character would never trade for safety. Then bring those answers back near the ending.
The 6 to 10 sessions length feels right for Atlantis Beneath the Tide. Enough room to build suspicion without losing the thread.
I ran something adjacent to Atlantis Beneath the Tide, but the party trusted the wrong faction almost immediately. I would keep that possibility open here too.
I would open Atlantis Beneath the Tide right in Mythic Mediterranean and let the party find the first clue before anyone explains it.