In the skies of the Narnian world, there were magical sentient beings called Stars that brightened the night-time sky of the dome (the Narnian world also contained a Sun at day and a Moon at night). Below the world's surface there were also habitable nations, which sustained populations, such as Underland of the Shallow Lands, and Bism at the the world's base.
On the other side of the unnamed continent, was the Western sea that contained the unexplored Western Islands, which possibly were on the coast of Telmar, and presumably had a Utter West at its edge. Beyond the edge of the world, in all directions, including altitude, was Aslan's Country that ringed around the whole world of Narnia, and indeed also above its sky.
Creation of the World of Narnia
See also Narnian Ages
The World of Narnia was a disc-shaped world (unlike Earth, which is spherical), with the sky like a great dome that met the world around its circumference, on which the other side, and indeed all around the world's edges, was the mysterious land called Aslan's Country.
The guardian and creator of the Narnian World, with the help of a few people, was the Great Lion, Aslan, who sent people (mostly children) from our own earth on missions to save Narnian society from destruction.
The Creation of Narnia was witnessed by six creatures; Jadis, the former Empress of Charn; Digory Kirke; Polly Plummer; Andrew Ketterley; Frank, a cabby; and Strawberry, his cab-horse. This group was brought to the unmade Narnian world by accident, during a failed attempt by Digory to transfer Jadis from London, in our world, back to her own world of Charn.
Aslan began the creation soon after they had arrived, using song to call forth the stars, sun, and eventually all land-forms, plants and animals as well, which came from all around them, as well as underneath them. When he was finished, Aslan selected certain animals to be Talking Animals, giving to them, and all other magical creatures, Narnia as their new home.
Aslan next anointed its first rulers, who were the cab driver and his wife (who he had called to Narnia), King Frank I and his wife Queen Helen, and commanded them to rule peacefully over the Talking Beasts. Aware that the evil witch Jadis had entered his new land, Aslan sent Digory on a mission to retrieve a magic apple from a garden located in the Western Wild beyond Narnia. When he returned, the apple was planted by the river, where it immediately grew into a tree that, as Aslan explained, would protect Narnia from Jadis for centuries.
Aslan allowed Digory to take one of the apples from the new tree back with him to our world for his ill mother. After she had eaten it, she recovered from her illness, and he planted the core in his garden, where it grew into a great apple tree. Many years later, the tree was blown down in a storm, and the now Professor Kirke had its wood made into a wardrobe.
The Destruction of the World of Narnia
2555 years after Narnia's creation, the world of Narnia was destroyed after the ape Shift attempted to deceive the inhabitants of Narnia into thinking that a donkey, Puzzle, was the actual Aslan. Shift also made an alliance with Calormen, and ended up inadvertently summoning the evil god Tash.
After a long, terrible battle with the Calormenes on Stable Hill, Tirian, Jill Pole, Eustace and the Rishda Tarkaan were thrown into the stable. Tash captured Rishda and took him away; Tirian and the Seven Friends of Narnia watched as all the inhabitants were called into the stable (which was actually the real Narnia), the Stars fell from the sky, the vegetation was destroyed, and the whole world flooded. The giant, Father Time, then destroyed the Sun, and Narnia completely froze over and ended. However, they soon found that this Narnia, from the dawn of time, was really just a mere copy of the real one, which, along with all the other "real" worlds, branched out from Aslan's Country.