I'm in the early stages of writing a fantasy story set in a different universe. The place where the story takes place is the only world its inhabitants have ever known. Consequently the laws of nature there seem as though they are the only way things could ever be. However, those laws are very different to the laws of nature as they exist in our world.
To begin with, there is no curvature to the horizon. It isn't one of those flat disc type of worlds like the one in Terry Pratchett's books. No, this is an even stranger world which exists in the form of an infinite ocean. There is no edge to fall off of. A ship could sail as far as you like in this other world and would still never fall off, but neither would that ship ever return by circumnavigation. Instead, the ship would sail on and on and on, forever.
There are continents and islands upon the infinite sea, and people living there.
The story I'm writing begins with a sailing ship setting out on a journey to discover new lands. The crew are from a country called Strakk on the continent of Zaquerral. Their civilisation is at about the same level of technology as Europe in the 18th Century but, as they journey across the infinite ocean they will eventually discover other continents where the societies are simpler and some where the technology is more advanced. Some where on that infinite ocean are people with technology resembling the 21st Century of our world and some who would appear to us to be futuristic.
The sea goes on forever in all lateral directions. The sky continues infinitely upwards and the ocean continues infinitely downwards. There is no bottom to the ocean and the land masses continue infinitely downwards too. It is possible for such a thing as a bottomless pit to really exist in this world of wonders.
The days are illuminated by the SunMoon, a mysterious orb which hangs in the sky at a very great altitude and radiates great heat and light from one side of its surface but glows more darkly from the other side. The SunMoon slowly rotates, providing 18 hours of daylight and 18 hours of nighttime in every 36 hour cycle. There is also a variation in the glow emanating from the SunMoon's darker side and this variation corresponds to five 'phases' of the night.
Scientists on some of the continents have constructed theories to explain how the SunMoon stays up in the air, or what may lie beyond it. None of these theories is yet proven.
There is no 'navigating by the stars' because there are no stars and the strange, flickering colours which appear in sky at night appear to be random.
The main characters set sail for adventure, with no plan of returning home ever again. For good or ill they have all given themselves up to a life of new discoveries.....