"Hey, it's a piece of map! Hold on, this is Fred and George's handiwork. The map shows there is a forgotten area around here. I wonder if it could be behind that old rusty door? The map says there is a magic word to open the door. Well, here goes... ALOHOMORA!"
Ronald Weasley about the map[src]

This map is a piece of Charmed parchment, on which Fred and George Weasley charted the Forgotten Grounds, and instructions on how to get in there.[1]

The twins left this map tucked inside the Hogwarts Library's copy of Quidditch Through the Ages, which eventually found its way to Harry Potter in 1991. When Severus Snape confiscated the book from him, Harry and Ron noticed that the piece of parchment had slipped from the pages, and used it to go into the Forgotten Grounds.

Given that Fred and George Weasley had the Marauder's Map at this time, it entirely plausible this is a part of it.


Notes and references

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