In third year, when Harry is denied access to Hogsmeade, Fred and George make things a little easier for him. They gifted him a parchment, but not just any parchment. With a declaration of nefarious intent, a map of the school and all its current inhabitants appeared. Harry was now able to follow one of the many secret passages to sneak out to Hogsmeade under his invisibility cloak, and he certainly found a great many other uses for the map as well. Good thing Messrs Moony, Wormtail, Padfoot and Prongs knew just how to keep Snape's prying eyes away!
Experience a little Marauders' magic with this cool change glass. No wand needed, simply pour in your cold drink as you speak the words 'I solemnly swear I am up to no good'* and watch the Marauders map appear.
*Disclaimer: enchantment not actually required to summon the map on this glass!