This unique treasure is found in the Treasure Room of the Cavern of the Gods using the clues from the treasure rumor titled "Okeanos Tablet 5" in the player's notebook. However, the player must first have completed the map of the Cavern of the Gods.
The appraisal reward for finding this item is sixty-five thousand pelagos, making it by far the most valuable salvage item in the game. Nancy Young also gifts the player the Alloy Tank, a piece of diving equipment, for finding this treasure.
Relevance to Money-Making Post-Game
[WARNING: This section contains spoilers relevant to the post-game section of Endless Ocean 2.]
The player is indeed able to find this treasure before the end of the main plot, making it a good device to start the money-making quest that is re-opening the Cavern of the Gods in post-game. As was stated before, the player must have first completed the map for this treasure to be available. In order for the map to truly be registered as "completed", however, the player must consult Oceana after filling in all of the map's tiles so that they can get the money for completing that map.
This is easily done if the player simply explores all of the hallways, explores all of the altars, explores both the Pillars of Light and the Pillars of Shadow, and makes sure to explore the Subterranean Reception Room. This will fill in all of the map tiles without the player having to enter the Celestial Mausoleum or any of the upper floor at all.
Once the player has told Oceana about the completed map, this treasure rumor will be active. Once the player finds the Pacifica Treasure in the Cavern of the Gods, as long as they have properly activated the treasure rumor, they can enter the Treasure Room, use the Multisensor, and retrieve the treasure before their time to escape runs out.
However, some players have reported a glitch where none of the prerequisite cutscenes will activate if they leave and then re-enter the Cavern of the Gods before having found the Pacifica Treasure, so it is advised that the player attempt this strategy with caution.