Submerged Superstructure

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

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

It is implied that the explored the Submerged Superstructure themselves, as the Cloak found inside before the '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 Echo 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. However, the player can use their tongue and/or the low gravity in LttM's room to exit through the pipe at the top of the room. This will lead you to the top of LttM's superstructure. To the right is the one way gate out of the Submerged Superstructure, while to the far left past the 5 Natural Urges imagery is said echo.

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  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 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 s. This area serves as one of the locations featured within the ending sequence for '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 is expelled to after restoring power to 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 scavenger 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.