Rowling's imagination didn't stop with the main hall. She treats us to moving staircases, talking portraits, an elaborate prefects' bathroom, the Room of Entitlement (providing just what you need at critical moments in the plot), and huge chamber-like classrooms filled with dinosaur skeletons and mysterious cabinets. Dumbledore's office is a wonderful mix of messy and marvelous. Books totter in haphazard stacks and tumble from shelves. His desk is littered with papers, candy and mugs. Colorful vials sparkle from one glass cabinet. Behind another, a large bowl contains memories too painful to bear. And on a perch overseeing it all, sits Fawkes, Dumbledore's phoenix.
Eventually we step outside the castle to the grounds and we encounter the Whomping Willow (a shuddering tree that snaps birds from the air and wallops passersby), an ornate covered- bridge spanning a breath-stopping chasm, The Forbidden Forest, where centaurs and giant spiders roam, the Quidditch field and Hagrid's Hut where the groundskeeper nurtures baby dragons and such. The setting is enormous. I haven't even mentioned Diagon Alley, Hogsmeade, The Burrow, or The Ministry of Magic. It boggles my mind that this world sprung from Rowling's head. And now it lives on in books, movies and websites. For a detailed look at the Potter world, see The Harry Potter Lexicon.