The Sunset
"Until when he has come to the setting of the sun, he sees the sun setting in a sea of muddy black, and he finds there a congregation of people: We say: O Dhu al-Qarnayn, you may torture or may do good to them. (Sura 18:86)
The verse describes Dzulkarnain, a traveler. The sun there is the sun IN THE VIEW OF A HUMAN ON THE EARTH, Dzulkarnain.
Drowning is the meaning of the kias, which signifies the day is late afternoon. Just as if you go to the beach, in the afternoon the sun as if sunk in the sea (Sunset). This indicates that it was evening when Dzulkarnaen arrived on the shores of the Black Sea.
The phrase 'aynin hami' in the above verse which consists of the word 'ayn' = springs' and 'hami' = mud. This may mean a less obvious view or a visual trickery. So the meaning is clear from the phrase "the sun is found buried in a spring of muddy black" is found, "here" is Zulkarnaen, so Zulkarnaen see a less clear view or the sun's visible trick into the spring.
If we see the sun set on a television screen just like seeing the sun sink in the sea. The colors on the screen change as the sun sets over the sea, it looks grayish on the television screen. Therefore, for people who see this, the landscape looks as if it is drowning in a sea of muddy black. In addition, this verse relates to the existence of this part of the world. When the sun in one region of the eastern world sank to the west, then in the sunset itupun we will find a group of humans in the western hemisphere and here we will find the sun even rises.
So the above verse actually explains about time. The time of day is late. That when Dzulkarnain arrived at the edge of the Black sea he saw the Sun sink (Sunset).