I really love the continent Zammonien from the books by Walter Moers, like "The 13½ Lives of Captain Bluebear". Just to give you an idea: In one life bluebear goes to nightschool - a school in a mountain lead and taught by an Professor Dr Nachtigaller, who has 7 brains - together with a moutain demon (kind of) and a prince from the 2364. dimension (where everything is made of carpet and people make music on instruments made out of milk) named Qwert Yuiop. Later bluebear gets to the sweet desert, which isn't filled with sand but with sugar. For the nomadic people of the sweet desert he catches the half-stable fatamorgana City "Anagrom Ataf" in a big pool of molten sugar. You get it. Bluebear being the kings of lairs at one point in the book really fits.

Moers wrote multiple books about that continent. I really love them. I just organized a big station based game about that for my local scouts troop. About 60 kids from 7 to 16 years following my story to rescue Zammonien. Easily dumped 150h of work in that game, but it was really great

Boring answer, but probably Middle-earth/Arda. Just such a well-crafted world with deep and interesting lore.

Runner up would be Bas-Lag from China Miéville's books. Very unique, somewhat Lovecraftian steampunk world with many weird inhabitants.