Hogwarts Castle is a castle on the map by Gabbel. This version has been completed with over 400 unique rooms, halls and corridors. The castle was heavily inspired by the Harry Potter movies, but it has been newly and rearranged architecturally and the creators have added a few things. The map only features the castle itself (no forests, Quidditch pitch, etc.), but almost all the indoor locations mentioned in the books and movies. Naturally, there seem to be plenty of secret rooms and Easter eggs, and for those who really enjoy exploring, there's a scavenger hunt with prizes that write themselves in as befitting a Hogwarts student!
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