The Great Aqua Cave, also known as the Mermaid's Tunnel, is a long, twisting cavern found in Endless Ocean.

Flora, Fauna, and Geography

Local Life

The rooms of the Great Aqua Cave are home to many unique forms of sea life, including a resident False Killer Whale, a small herd of West Indian Manatees, and a trail of Blue-Spotted Lagoon Rays leading the player back to the entrance from many places in the Cave.

There are also other forms of life here, like Longtooth Groupers, John Dory, Marbled Rays, Threadfin Butterflyfish, Yellow Boxfish, and Blackspotted Puffers. During the night, a Pelagic Thresher patrols the tunnels.

Location & Geography

The Great Aqua Cave can be accessed if the player swims through Mermaid Tunnel, which is located at coordinates L-7, in the southeastern area of the Manoa Lai Sea.

The static treasures found here are the Patterned Pottery and the Iron Pearl of Manoa Lai.


Stalactite Labyrinth

This is a large room with stalactites reaching from the ground to the ceiling, hence its name. There is a slight difference in the fish that appear here at night - a Longtooth Grouper appears here after dark, while in the daytime it is absent.

Great Column

This is a small room named for the columns in it. Many shoals of small fish live here, and the player can find a piece of the Patterned Pottery laying on the floor. Other than the small fish and the Pottery, nothing much of interest appears to be located here.

Rim Pool

This is a fairly large one, home to a small herd of West Indian Manatees and a few shoals of much smaller fish. Its formation is also unique; the seafloor here is not smooth, but instead, rounded tiers of rock. A waterfall located directly above it masks the entrance to the White Room.

White Room

The White Room is named, rather obviously, for its white walls and stalactites, presumably made out of limestone - the rock first mentioned in the email the player receives that talks about Great Aqua Cave.

In-Game Dialogue

Before the player can go diving in the Great Aqua Cave, they must have visited the game's Aquarium at least once after unlocking it, which then unlocks the underwater camera and triggers an email alert from Douglas Banner. Depending on how the player chooses to explore the map, it is possible to find the cave's entrance prior to this, but Katherine will forbid them from swimming inside. The email goes as follows:

"Subject: The mermaid's legend!

From: Douglas Banner

Yo! Guys! Ever heard of the White Cave?

I've been reading the journal of Arthur Edward Fisher, the explorer who discovered this island, and he wrote about this local legend:

Long ago in Manoa Lai there was a castle that sank into the ocean after an earthquake. The queen fled into a white cave, but it was also taken by the sea. And there the queen became a mermaid.

I'm totally into the surrealism...

Anywho, I'm thinking of writing about it for my next article, but I don't have enough to work with. Lemme know if you find the cave, okay?

Peace out!"

After this email, Kat will approach the player and note that a "white cave" would likely be made of limestone, and that there's a lot of limestone around the Southeast area of the map. Then, she'll give them basic cave-diving instructions so that they can enter the cave, if they find it.

After the player has found the cave and returned to the boat, Kat will say:

"Hey, you made it! ...I mean, welcome back!

That cave was incredible! I can't believe it really exists! When we tell people about this, they're going to freak out. Maybe they'll let us NAME IT!

Let's see...Katherine Cave? Great Katherine Cave? Hmmm…

Hee hee! I'm just kidding!"

The player will subsequently receive two emails, one from Douglas Banner and one from Alfred Thorman.

"Subject: You RAWK!

From: Douglas Banner

You found the White Cave? That's AWESOME. Now I can write my article! Thanks, guys!

Oh and hey! I did more research about the legend of the cave. Check this out:

The only one to escape from the cave was the queen's attendant. She was led out of the cave by a spirit appearing in the form of a green flame that guided her to the exit.

Could that green thing have something to do with the cave? Hmmm...

Well, I guess you can always follow it if you get lost! Ha ha!

Peace out!"

"Subject: Undersea Cave Discovery

From: Alfred Thorman

Once again, well done. It is hard to imagine that such a huge cave has gone undiscovered for so long. Perhaps it truly is the white cave from the ancient Pelago myths.

Katherine is keeping me updated on the progress of the discovery. It seems we still have much to learn about the depth and structure of the cave.

Again, I have nothing but the highest respect for your work up to this point. Make sure you get enough rest, and keep up the good fight.

-Alfred Thorman"


  • The entrance to Great Aqua Cave from Mermaid's Tunnel.
  • The diver entering Great Aqua Cave during a cutscene.


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