Wrecked submarines occasionally spawn on the seafloor of Europa, wherever it may be.
Cold Caverns[barotraumagame.com] has an exception to wreck spawns, that being they can only spawn in the "transition" subtype which has a minimum difficulty of 10%. Any biome farther than the Cold Caverns can spawn wrecks regardless of subtype.

The method I use to find wrecks is to be close to the seafloor and use the active sonar[barotraumagame.com]. If a wreck is present, a subtle outline can be spotted.


Once the suspicion of a wreck occurs, get close to the wreck and use the passive sonar.[barotraumagame.com] The wreck should show up on the sonar as if you were to use the passive sonar on the start outpost or end outpost.

Thalamuses can sometimes be present in the wreck, thalamuses do not appear visually different from a wreck, so exercise caution when approaching wrecks.
Thalamuses do not spawn in the Cold Caverns, any biome farther than Cold Caverns can take place.

Upon discovering that the wreck you found is a thalamus, the flesh gun[barotraumagame.com] will hit your submarine and pull it towards the thalamus. The flesh gun does not pull the thalamus towards the submarine regardless of size difference. Destroying the flesh gun's ammunition[barotraumagame.com] removes the hook and frees your submarine, allowing you to gain distance from it.


Thalamuses will use the turrets on the wreck to shoot at the submarine. Their offensive attacks are dependant on the size of the wreck, where it may have a flesh spike[barotraumagame.com] to cut through the hull and inject terminal cells[barotraumagame.com] into the submarine, which for any unfortunate submariner in proximity to a terminal cell will detonate it and cause a flash of light, hull damage, and acid burns[barotraumagame.com] to any nearby submariners. They are easily killed (10HP) with the most effective choice being fire, melee is not advised.


Upon entering a thalamus, their immune system, or defence, the leucoyte[barotraumagame.com] are present in the thalamus which will attack any invaders. Their attacks cause acid burns similar to the terminal cells, however they also cause paralysis[barotraumagame.com]. Leucoyte come from cell spawn organs[barotraumagame.com], the amount it can spawn depends on the difficulty.


The thalamus' brain[barotraumagame.com] is the number one target of the thalamus. Once a thalamus brain is destroyed, every other thalamus part dies with it, and the wreck is set free of thalamus control.