Rose and the astral construct dunk their heads below the surface, the construct swimming as Rose settles to the bottom, and slowly walks on the bottom. As Rose moves further, she realizes the water is too dark to see [Assuming she breaks open a sunrod], the astral construct taking off without her, swimming without issues in the now placid water.
The first largest room, contains 2 walls north and south, that look like privacy walls. 4 pillars stand equidistant to one another, each with a spigot at the top about 8 feet up, a center stone, that rises only a few feet, also contains several spigots. This area is open and leads to 2 other rooms east and wast, and a 3rd barred room to the south.
The room to the east:
This small room contains four long benches and several niches along the walls. A pile of bones and it's equipment lie in the corner of this room.
The Astral construct swims off, doing as commanded.
Spoiler
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Rose held breath: 3/28 rounds
This water is all the way to the cieling, so you will be completely submerged, I got the impression that you thought that was not the case DrK? If not, you can tag along, but if so, feel free to change your mind. Though, you would be moving at half speed, so 10' (and can hold your breath just as long)
Spoiler: Things
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Attack - (1d20+2)[20] vs 16
Damage - (1d6+1)[2]