There are plenty of side quests in Hogwarts Legacy, most of which take place in and around Hogwarts. Several of these side quests become available after players have returned to the castle following their first visit to Hogsmeade, including one called "Cache in the Castle." This takes the form of a treasure hunt, with players simply needing to follow a few clues in order to find a hidden chest.
The quest is handed out by Arthur Plummly, a Hufflepuff student who can be found hanging around in the Defense Against the Dark Arts tower. Speaking with Arthur will lead to Hogwarts Legacy players being given a treasure map with three clues drawn on it: a rhino skeleton, a dragon fountain, and a mysterious-looking painting. To find the treasure, players will first need to find these three things.
Where to Find the Rhino Skeleton in Hogwarts Legacy (Cache in the Castle)
The first clue needed to complete the "Cache in the Castle" side quest in Hogwarts Legacy is not too far from where the side quest first begins. To reach it, players will simply need to head down three floors using the staircase near Arthur. Then, they'll want to follow the path around to their left and head down the central staircase on their left, at which point, the rhinoceros skeleton will be in front of them to the right.
Where to Find the Dragon Fountain in Hogwarts Legacy (Cache in the Castle)
Players don't actually need to do anything with the rhino skeleton; just walk up close to it until a new quest prompt appears on the screen. Once it does, they'll be tasked with finding the dragon fountain, which is located in the Transfiguration Courtyard area of the Astronomy Wing. If players have already unlocked the Floo Flames location in the courtyard then they can fast-travel straight there. If not, however, they'll need to set a waypoint and head there on foot.
Where to Find the Painting in Hogwarts Legacy (Cache in the Castle)
After getting close to the fountain, players will be tasked with finding the third landmark, which is through a pair of double doors to the northwest of the fountain. After passing through them, players should head up the staircase to their right, which will lead them straight to the painting from Arthur's map. As per the clue on the map, players should use Accio on the symbol at the top of the painting's frame, which will enable them to get to the secret chest hidden behind it.
How to Complete the Cache in the Castle Side Quest in Hogwarts Legacy
Opening the chest will reward players with the Authentic Historian's Uniform: a cosmetic item that players can use to customize the playable character's appearance. With the mystery now solved, players should head back to the Defense Against the Dark Arts tower and report in with Arthur. Doing so will complete the quest and players will be awarded 180 XP for their efforts. They'll also get to keep the historian's uniform that they found earlier.
Hogwarts Legacy is available now on PS5, Xbox Series S|X, and PC. PS4, Xbox One, and Switch versions are currently in development.