Meanings of sunless sea in English

Don't you remember how we had to go downhill to reach the sunless sea?

The dark mountain road, the sunless sea.

The river you hear is swift and black, and flows down and down to a sunless sea.

We wondered whether there were any actually igneous manifestations below, and whether the waters of that sunless sea were hot.

Visions of another Albion -"Where Alph the sacred river ran, through caverns measureless to man, Down to a sunless sea."

For thousands of years every philosopher had stood on the shore of this sunless sea, diving for pearls and never finding them.

Many graphic sculptures told of explorations deep underground, and of the final discovery of the Stygian sunless sea that lurked at earth's bowels.

In February, 1856, the Pacific, from Liverpool for New York, carrying 185 persons, passed away down to a sunless sea.