The world is a little bit like an inverse onion. As you travel further in, each ring is larger than the last.
What little is known about the grand structure of the universe comes primarily from the enigmatic being known as Merlin, who’s said to be older than the Earth itself and claims to hail from beyond the stars.
There are three known layers. The innermost layer is the observable universe, composed of stars and galaxies and planets. Even Merlin does not know if there’s a genuine edge to the expanse, but if there is, it’s probably at least a hundred billion light years out from Earth, and likely much further.
Beyond the stars lies the world of Heaven, which Merlin refers to as a city. It is not a human city, though a few humans do dwell there. The city is built at the foot of a great mountain range that cuts across the world, almost dividing it in half. Altogether, this layer is like a galaxy-sized plate world with the sun in orbit around it; beyond the plate, there’s nothing but emptiness. Or at least, no-one daring to venture out that far has ever discovered anything. It’s possible to enter the next layer, where Earth exists, via some caves in the mountain near Heaven; however, due to the vastness of the universe, that won’t get you anywhere interesting.
But beyond the void there’s yet another outer world, the world of the Golden Tower and the Four Cities built by the same race that later founded Heaven. This world is a great cube, dominated by the massive Golden Tower at the centre amidst a huge desert. The sun hovers high above the cube, traversing a path around the tower’s tip. As a result, night here is literally just the shadow of the tower. The four cities are all built near the tower - Gladon is built right at the tower’s base along one side, the other three are much further out forming a triangle. Clamparo sits at the base of a mountain range on one side of the desert, Anaglosia straddle’s the desert’s nearly-opposite edge, and Strondan is a coastal city not that far from Anaglosia. The next layer, where Heaven is, can be entered via a circle of standing stones near Anaglosia. In addition to the cube-world, there is a single distant galaxy and a handful of somewhat closer stars. If you were to travel to the galaxy and then just keep on going in the same direction, you would pass through it and then end up back at the cube.
Some have speculated that the tlalfarans, a mysterious extinct species of which almost nothing is known besides their name, may have come to the world of the Golden Tower from yet another layer further out. However, no concrete evidence of this theory has ever been found.
Some years ago, someone I knew on a now-dead forum was nice enough to draw a rendition of the city of Anaglosia, which I’ve posted here for the curious. It’s little more than a concept and probably not super-accurate, but it may give a good idea of the scale of the tower.