"Nikki Gamble distinguishes three subtypes of High Fantasy...A distinct world-within-a-world as part of the primary world (e.g. Harry Potter)"

"In the case of a world-within-a-world, the secondary world co-exists with the primary world; however the mundane inhabitants of the primary world are unaware of secondary world, with unexplained happenings rationalised into things they can understand. The Harry Potter series is again set in the real world; however, the primary setting, mostly the school Hogwarts, is said to be located in a secluded place in Scotland, but is physically separated from the real world and becomes a "world-within-a-world." Hogwarts is therefore as much of an alternative world as C. S. Lewis' Narnia, which means that both series are in the high fantasy subgenre."