Ashika Island is full of secrets. Under Tsuki Castle on the Waterways you can find a secret bunker, getting inside is fairly easy and yields and decent amount of loot.
Under Tsuki Castle on Ashika Island you'll find a network of waterways that lead out to different parts of the island. Handy if you are trying to rotate and change position or stay undetected while you move around the map. You may have noticed some blast doors that will be familiar to those who played Verdansk.
At one stage in it's life there were multiple bunkers scattered across the city of Verdansk that players used to line their pockets with the absolute best loot. Well, Ashika Island also has one of these top secret bunkers, and getting inside is a fairly easy task.
If you drop down below Tsuki Castle you'll come to an open space underground, they'll be a submarine sitting in the water among other things. You can't really miss the huge blast doors.
How to get into the Secret Bunker
Note: We've added a video guide at the bottom of this article if you'd prefer a visual representation.
The first step is to get yourself to the correct location. The Secret Bunker is underneath the Castle. Look directly at the doors and drop into the water to your right. You'll see 2 underwater vents, the first that you come across is blocked with a metal grid. Move over to the second vent to the right. The metal grid on this vent is broken.
Swim in the vent but take care, if you are the first person into the bunker there will be 2 booby traps you need to defuse. One at the entrance of the vent and one at the end, defuse both and keep swimming.
You'll need to pop up for air at this point and when you do you'll notice a pillar in the water. Climb to the top of this pillar and parkour jump your way across the remaining pillars. This will lead you into the Secret Bunker. It contains a fair amount of orange loot chests and other lootable furniture.