This is the first of Robert Silverberg's Majipoor series. It is set on a planet called Majipoor, a very large planet that has been settled by humans and has other creative races living there. It is a classic of fantasy.
Majipoor was home of the Metamorphs before the humans arrived. The Metamorphs are Shape-shifters, humanoids who can change their shape. Other races include: Skandars, four-armed hairy tall humanoids. Ghayrogs, reptilian people. And Hjorns and Vroons, which are dwarfish with strange beaks or tentacles respectively.
The planet itself is huge. There are three main continents. They are each described lushly throughout the book, as the main character, Valentine, goes through a large bit of it.
One of the most interesting parts is the continent of the political leaders, a continent called Alhanroel.
On Alhanroel, the Pontifex, who is the highest official of Majipoor, lives underground in the Labyrinth. Up the river is the massive Castle Mount. There, at the top of a mountain surrounded by 50 great cities, is the Castle where the Coronal rules from. The Coronal is like the figurehead ruler. A king of sorts.
The plot of Lord Valentine's Castle is that Valentine has been usurped by somebody, put into a new body with no memory of his past life. He learns in his dreams that he was the Coronal before he was put into a new body. Thus, his quest begins to reclaim his rightful place as Coronal of Majipoor, Lord Valentine.
On the course of this journey Valentine becomes a traveling juggler in a troupe. He makes lots of friends and meets his lover. The journey is certainly an epic one.
People often say the world-building is the star of Lord Valentine's Castle. They're not wrong. But there is much more to it than that. The story itself is compelling. However, there is a large world-building component as well.
I really enjoyed Lord Valentine's Castle. Highly recommended!