Brine Star: Secrets

You can find a few extra chests inside a hidden room in Brine Star, but the most important secret is the Svetlana Twofeather room. There, you can find a unique augment: the Spring Augment. To reach Svetlana's room, you will need a very unusual item: the Relocator. You will also need the Sonic Sphere tech to reach one of the hidden rooms.

Ixodoom husbandry area
In the hive blocks area to the left of the first boss, the first boss, you can find a small opening to the far left of the room. You can use a Sphere tech to crawl inside. A metal door will block your way there. Despite not being a Red Door, explosives worked to open it in my case (i used the alt shot of the Hellfire Bow). You will then reach a small hallway with a red pressure plate briefly opening the door to the left. Charge your Sonic Sphere on the pressure plate and you should be able to cross the door before it closes. Behind it, you will find a chest and some Ancient Essence.



Hidden room to the right of the first boss
Near the right entrance of the first boss room, you can find a small hallway covered in thorny bushes. You can use the Spike Sphere tech to cross it. In the middle of the hallway, you might notice the absence of bushes and a ground made of different blocks. Exit your sphere above those blocks and interact with them to open a small room containing some Ancient Essence and a console to exit the room to the left.



Top of the swamp water pond
If you head to the left in the second part of Brine Star, you will reach a swamp water pond. If you cross it to the right, you will find a small house with 1 melee and 1 ranged Floran inside. To the right of that house, you can see a wall with flowers blocks. Dig those blocks with your Manipulator and you will reach a small room containing some Ancient Essence. However, the door will close behind you and you will have to defeat 6 Minions to reach most of the Essence and exit the room.



Depth of the swamp water pond
If you dive in that same swamp water pond, you will first reach the room with the turrets on the side. After crossing that room, head to the left where you'll be attacked by 6 giant fishes. You will then reach a room with a laser beam on the roof and a chest behind them. I guess the beams are supposed to be activated when you reach the room and that you need to shoot the explosive barrel on the other side to turn them off, but they were never activated in my game.



Svetlana's room
To reach Svetlana's room, you will need to activate 4 proximity detectors scattered through the dungeon. You can know the detector got activated when you see the torch near them light up.

First detector
The first detector is located at the beginning of the dungeon. After falling in the water pool where you have 2 paths available to you, head to the left. You will reach a small wooden bridge crossing a poison pond. Use your Matter Manipulator to dig the flowers block inside the poison pond and you will reach a small room where you can find the 1st detector.



Second detector
The second console is also located near the beginning of the dungeon. After falling in the water pool where you have 2 paths available to you, head to the right this time. You will reach the area where you have to cross a door before it closes again. If you go through the exit to the right instead and cross the hallway with falling boulders, you will reach a room locked by a Red Door. Blow the Red Door with explosives and you will find a console to activate.



After activating that console, head to the healing water pond a bit further. Use your Sphere to crawl through the small passage in the pond. It will lead you to a room with some Ancient Essence. Use your Matter Manipulator to dig out the dire stones in the wall to the left and you will reach the room with the second detector. Be careful in that room, a pressure plate in the middle of the room will drop bombs on you if you trigger it.



Third detector
A book found inside the dungeon gives you a hint on how to reach this detector.

To reach the third detector, you will need a quite unusual item: the Relocator. In the crossroad after the first boss, head to the right until you find a Red Door. Blow it up and you will reach a room with a console in the middle. Activate it and some platforms will start to appear/disappear above you. Climb your way to the top right of the room using those platforms and you will find a small room with... bunnies. You will need to grab one of these bunnies with your Relocator (right-click to grab it).



After grabbing a bunny, head back near the elevator that you took from the first boss. You will find some platform leading you to a small room to the right of the elevator. Drop the bunny (left click of the Relocator) in the bowl above the lava then press the button on the wall. The bunny will fall into the lava and a hatch will open to the left of the room. Crawl down the path under the hatch using your sphere and you will reach the third detector. Be careful when exiting the room after activating the detector, the floor will open under your feet and there's a pool of lava below. Use some lava immunity or do not fall into this trap.



Fourth detector
The last detector is located behind a small puzzle. Head to the path to the right in the second part of Brine Star (the stairs are just in front of the Red Door leading to the bunnies for the 3rd detector). You will reach a small puzzle room where you have to guide the water to the second pit from the left using the consoles. There are different consoles combination that works, but activating the 1st and the 3rd console from the left then pressing the central button will work. The last detector is in the room that opens to the right.



Last puzzle room
After killing the final boss of Brine Star, exit its arena and head down the platforms near the Terraforge. If you activated all 4 detectors, the 4 torches should be lit and the door opens. Following the hallway, you will reach a large room with a statue (representing the Cultivator or a Chozo statue from Metroid) and a lava pool. Listen to Baron and climb the statue. You will need to stand inside the hand of the statue, under the galaxy hologram, to start draining the lava below you. Once the lava is fully drained, a door will open to the left of the pool, leading you to a room where you will find Svetlana. In the room behind Svetlana, you will find a chest where you can find the Spring Augment. Picking up the augment will also unlock it in the Nanofabricator. You will also find 2 other chests behind the one with the augment, as well as a teleporter to exit the dungeon.