The Glimmersea

The Glimmersea is a colossal underground sea nestled deep in the Lowerdark, the lowest section of the Underdark, 20 miles directly below the Sea of Fallen Stars. It is often referred to as the Sea of Starry Night due to some portions of the Glimmersea having luminescent rocks and fungi that shine like stars, and illuminate the vast underground sea. The light from these rocks & fungi are reflected off of the water, and it looks like you are sailing through a sea of stars (hence the nickname).
The cavern in which the sea is located varies in height, but averages around 700 feet high. There are dozens of massive natural pillars, some of them hundreds of feet in diameter, that connect the bottom of the sea to the ceiling which prevents the cavern from collapsing on itself.
There are sections on the ceiling where the water from above has eroded a path making its way down to form waterfalls. The true size of the Glimmersea is somewhat unknown as the cartographers who have attempted to map its borders have either been driven back, or have been taken by the dangers lurking both above and below its depths.
There are full underwater cities located in the depths of the Glimmerse. Most have been abandoned, but some house populations of Aboleths.
There are a few brave sailors who venture out into the Glimmersea, most hailing from Azmar's Glow. They have their own methods of navigating and traversing causing others to hire their services out.
It would take a full 1-2 days of sailing to get across.

Type

Sea