Coral Basin is one of the primary sublocations inside Tidefall, and you cannot access it until you physically enter the cave system first.
Start by reaching Tidefall using a submarine or strong diving gear, then pass through the underwater waterfall that leads into the main cavern.
Once inside the central Tidefall hub, you will see multiple branching paths carved into the rock walls. One of these leads toward Coral Basin.
You should look for glowing coral formations and a slightly brighter underwater environment compared to the dark central cave. That visual difference is your main clue.
Swim in that direction while staying close to the cavern floor, because strong currents can push you off course if you go too high.
As you move deeper, you will notice a new region notification appear on your screen confirming you have entered Coral Basin.
At this point, the area is officially unlocked in your Bestiary and map progress.
Inside Coral Basin you will find unique fish, new crab cages, and special NPCs tied to future quests.
If you get lost, return to the Tidefall hub and follow the path marked by coral lighting rather than rocky tunnels.
Exploring Coral Basin carefully is important because several later objectives and hunts are tied directly to this zone.