Go to the Entrance Hall and head into the small custodian room to the left of the big exit doors. Cast Wingardium Leviosa on the mop and hover it over all the four odd tiles near the golden statue to clean them. You will earn Discovery Points and then Hermoine will talk, giving you 100% on the Marauder’s Map. Now go to the Viaduct Entrance and cast Wingardium Leviosa on the mop near the stairs. Use the mop to clean the odd tiles by the large staircase to earn more Discovery Points.