Livre 1, Chapitre 2: The Dark Tower
The Dark Tower is located in the middle of the Kalamaran Sea, it is where lost sailors end up when they are adrift in the sea. The tower is made of a strange black metal and is surrounded by slippery stairs that ascend its great height. Along those stairs, there are dark corridors that enter the tower into unfathomable darkness.
At the top of the tower, the roof is tiled with the symbol of an eyeless raven gripping a bloody eye, the Dark One's unholy symbol. Malgrave, a shadow spirit stuck between being too powerful to be human but not powerful to be a demon waits to serve the Dark One, an evil god of dusk, darkness and moonless nights. Malgrave uses the Dark Tower as a temple to his dark god and the area is considered unholy ground.
It is also possible that the tower is a gateway or portal to a realm known as the Shadowfell, and that some of the secrets of the tower are not of this world.
Purpose / Function
A temple to the Dark One that allows entry into his realm, it is a prison for Malgrave until he can get enough souls to ascend to daemonhood and serve Blacksoul directly.
It is also a link from the surface to the underdark, a perilous one.