In Harry Potter, there are clearly magical realms overlaid on the everyday muggle world, which are invisible/inaccessible to muggles, at least without magical intervention. Among them, I believe are:

• Diagon Alley
• Platform 9-3/4
• Hogwarts Castle
• The Black family residence at Grimmauld Place
• The Ministry of Magic

The Burrow (Weasley family residence, first seen in Chamber of Secrets) appears (on screen at least) to be a rather improbable structure, filled with magical artifacts (such as the family member "clock"). It seems to belong in the magical realm, yet Harry first encounters Ron on the muggle platform, having to traverse the portal to the hidden platform 9-3/4. Is the Burrow in the magical realm or the muggle realm?

Similarly: platform 9-3/4 is in the magical realm, but in Chamber of Secrets, Ron and Harry fly the car (in the muggle realm) from King's Cross station to catch up with the train, without explicitly crossing out of the muggle world. Does that place the Hogwarts Express line (and/or train) in the magical or muggle world?