The Marauder’s Map is a magical document that reveals all of Hogwarts School of Witchcraft and Wizardry. It is capable of showing every classroom, every hallway, and every corner of the castle, as well as the secret passages that are hidden within its walls. It also shows every inch of the grounds and the location of every person in the grounds.
The map was created between 1975 and 1978 by Remus Lupin, Peter Pettigrew, Sirius Black, and James Potter using the Homonculous Charm. The map also included a charm that caused it to display a series of insulting messages from each Marauder when attempted to be used by their nemesis Severus Snape.