Marauder's Map

The Marauder's Map was a magical document that showed the whole of Hogwarts School of Witchcraft and Wizardry: every classroom, corridor and corner of the castle, the grounds, the secret passages, and where every person on the grounds was, each shown as a dot with a name. It identified people correctly even through Animagus forms, Polyjuice Potion or Invisibility Cloaks, and it showed ghosts, Peeves and animals as well. It could not tell apart two people with the same name, and it did not seem to show unplottable rooms: neither the Room of Requirement nor the Chamber of Secrets appeared on it. Remus Lupin, Peter Pettigrew, Sirius Black and James Potter made it between 1975 and 1978.