Calyx is a disc world six thousand miles across. Both its shape and the nature of gods and spirits are inspired by the Norse myths, although it is definitely not a thinly disguised Earth setting. You won’t find analogs of the Germanic tribes, Celts, and Romans. The world is not shaped like Europe. On the other hand, my intent was to capture a world as the Germanic and Norse Iron societies imagined it: gods walk among the mortals, the worthy go to the halls of the gods after death, sacred spirits take their form in groves and rivers. There are hints of the Norse myths in the world but it is not a direct mapping of the known gods.
The history of the world spans 7500 years and there is a pre-history known to very few, not even the gods, that stretches much earlier. Like the Norse world, there was a creator Titan and in his death, his body become one with the world: in this case, he forms the immensely high central mountain range. At the time of Prince of Leaf and Stone, the world is still scarred by a cataclysm event that killed tens of millions and left much of the land infertile, although many islands of the old remain on the higher land. This cataclysm resulted in massive tsunamis that flooded much of the world and 120 foot tides that linger to this day.
In the world of Calyx, the sun is a few hundred miles across and orbits just outside of the disc, which makes for a very hot rim, in this imaging, hot enough to melt rock, at times.
The story in Prince of Leaf and Stone is not at all related to a D&D campaign, and would not serve very well as an inspiration for a D&D campaign but I have used the setting for D&D campaigns before. For those interested the setting and house rules, you can find it on wikidot.