Submerged Superstructure

The Submerged Supestructure is a late-game region added by the Downpour DLC.

Overview
Submerged Superstructure is the remains of 's superstructure, sunken beneath the 's waves due to the damage her can suffered in its legs after ' first attempt to expel the Rot. While it is best explored by the and plays an important role in their story, most  can enter the region if they have enough.

It is implied that the explored the Submerged Superstructure themselves, as the  found inside before the Rivulet's story has been given to Moon.

If the player comes here as the, a few rooms have been changed to make getting to The Heart easier, and they can find an additional inside of Bitter Aerie, commenting on their tenaciousness to get there despite the lack of a reward.

This Echo is not required for the Pilgrim passage, nor is it required to complete the Saint's campaign, and is incredibly difficult to get to without having completed their pilgrimage already.

The Heart
This area is the last stretch of the flooded underground portion of Submerged Superstructure, featuring a wide flooded conduit that leads into a central chamber for which the obtained by the Rivulet from Five Pebbles' infested can is to be relocated within this core reactor, in doing so restoring a fraction of the originally supplied power back to Looks to the Moon's facility and consequently spitting the player out into Bitter Aerie.

Auxiliary Transmission Array
An isolated high altitude tower that can be reached through the right uppermost pathway in Bitter Aerie, whose snowy skies are home to. This area serves as one of the locations featured within the ending sequence for the Rivulet's campaign.

Vents
This intermediary area contains most of the passageways within the flooded structure that have yet to be overtaken by the local flora and fauna.

Bitter Aerie
A cold desolate expanse that the Rivulet is expelled to after restoring power to Looks to the Moon's facility. The lower area contains partially flooded tunnels and pipes, while the upper area contains a series of ascents and descents through steep cliff-sides intermixed with wide surface areas exposed to the snow. In the west these paths converge together to lead to a one-way karma gate, the only and final exit out of this region, containing sparse life in the preceding mountains and passages underneath the surface.

Trivia

 * Submerged Superstructure has the acronym MS in game files, which stands for Moon Superstructure.