There is an ocean that never sees the sun.
It has no shore, this silent sea. No river feeds it, no rain falls on it.
Its waters are black, and not just because they roil sluggishly in endless night. Black and cold and as thick and salty as blood.
Every child on every world knows this ocean, feels it lapping beneath their bed in the deepest hours of the night. Every adult remembers it, feels its water in the cold sweat that beads their skin when they start awake from dreams too unbearable to recall.
Nightmares crawl out of that ocean. Fears slink into it. No light can illuminate it.
Older than time, it will drown the strongest swimmer and freeze the fiercest heart.
Speak its name and its waters will fill your mouth and throat and chest until you drown.
The Undersea, they call it in the city of nine bridges, the city that knows as well or better than any other that the tides of the blood need the greater tides of the ocean. The Undersea, that never ebbs or flows, deeper than death, darker than grief.
It has been a long time since anyone believed the Undersea to be anything more than a picture on the wall of a church, more than a tale that children use to scare each other.
Even so, it has never been quite forgotten.
You can hear the echo of its waters beneath the voices of the children as they sing their skipping rhymes on the bridges of Debreth. Once, twice, thrice lost, count, count, count the cost, still water, black water, see it take the river's daughter.
Beneath their feet the river rushes on, tumbling as fast through the city as the blood through their veins.
They laugh in the sunshine, secure in the knowledge that they are in the river and the river is in them, and all rivers flow to the sea.
But no river flows to the Undersea.
Its waters, black and cold and salty as tears, have no shore.
It is the only ocean that never sees the sun.