Do you know? The continent of Tivat, where we players are located, is likely to be underground, we are likely to be in a false world, and the so-called abyss may be the real starry sky.
According to the clues given by Mihayou so far, it is very likely that the Tivat continent where our players are located is in the underground world, and at the end of the story, our travelers are likely to spiral along the abyss to the real starry sky.

If you look closely at the moon in the sky, you will find that it is lower than Sky Island, and it will also cover sky island when it runs near Sky Island.
Of course, you may think that this is a BUG, but the name of miha tour this "detail demon" is famous in the industry, and the original god of this game in the place where we players can not see how much detail is also known, so this moon obscuring the sky island is most likely not a BUG, but Miha tour has another meaning...
On the other hand, in the previous story of the Fools, the Scattered Soldiers told the player that this starry sky is a huge lie, and Mona also mentioned that her master once said "False Heaven", which shows that many powerful people in the continent of Tivat have discovered the unusualness of this world.
So where is the sky that is being? From the current clues, the real sky is likely to be under our feet, and the deep spiral is likely to be the passage to the real starry sky.
We can corroborate this from Abedo's backstory. When Abedo once told the Monastery of Meru about true alchemy and mentioned that "the universe—the upside-down heavens, the strata—is a dream that time has forgotten," this sentence implies that the present world is an upside-down world.
In addition, we can also look at the description of the deep spiral: "We go to the universe, or go down to the abyss, there is no difference, because it is all unknown darkness." "Why can Miha you associate the Abyss with the Universe?" Coupled with the fact that in the abyss we can often see the starry sky and a bright moon, this hint is already obvious. At this time, when we think about Catherine's words that we will never listen to, "Toward the stars and the abyss", is it a little scary?
What exactly does the situation on the continent of Tivat look like? Where is the end of the abyss? Let's continue to look forward to it in the later plot!