Symbolism, Imagery, Allegory
Cair Paravel is the best real estate in Narnia: a palace on the eastern coast that's described as the true capital of the land and the place where the four Pevensie children will reign as Kings and Queens of Narnia.
Cair Paravel is as far east as you can get and still be in the land of Narnia instead of in the ocean. This seems to be important, because the east is somewhat holy—Aslan's father, the Emperor, is supposed to be Beyond-the-Sea, so Cair Paravel is made to commune with him.
Cair Paravel also represents a juncture between the natural world and the man-made one; although it's a palace, with a fancy-shmancy throne room and court, the eastern door opens right onto the sea and mermaids and mermen are able to swim close enough to the castle steps for their singing to be heard within.