You'll often be hunting down treasure in Hogwarts Legacy, as the whole map holds many hidden ruins, hamlets, caves, and more. Leaving these places unexplored would mean you will be missing out on a lot of opportunities.
In the side quest, 'Cursed Tomb Treasure', you'll receive a map that will lead you to a hidden treasure. But, you must first decipher this map to find where you'll need to head next.
Locate Manor Glen
To begin the Cursed Tomb Treasure quest, you'll want to make your way to the West Manor Cape Floo Flame in the southern area of the map. The quest will be northeast of here, in the Manor Glen area shown above.
Once you arrive at the broken down home, head down the stairs and enter in through the back entrance. Then, take a left and go down the stairs into the basement. On the left will be a door you can unlock with Level 3 Alohomora. Once inside, head down the hallway into the bottom floor and defeat the Inferi that appear in the area.
When you've defeated them all, make your way left into the next room and finish off the next group of Inferi. Then head forward through the doorway on the left. There will be two major enemies in this room, Lord of the Manor and Ailsa Travers. When you've successfully defeated them, you'll find a chest on the right side of the room that contains a map of the above image.
Tomb Of Treachery
The red X on the map depicts the location of the Tomb of Treachery, shown above. Use the Tomb of Treachery Floo Flame to arrive here, and head inside the underground location.
As you make your way inside, keep heading straight until you reach the room with a tomb and some bones in the middle. To the left of here, you'll notice a path blocked by a spider web. Use the spell Incendio or Confringo to destroy it, and then head down through here.
This room will have a few spiders you'll need to defeat. When you've done so, you'll notice a golden door just ahead with three missing butterflies. You'll need to find these three butterflies and return them to the door in order to open it.
To start, break down the spider web on the left and head down this path. You'll notice a box on the left side of the room that you can use Wingardium Leviosa on to move it in front of the large ledge and reach the top floor. There will be a butterfly up here that you can attract using Lumos, and then you'll want to return to the main room and bring it to the golden door.
The last two will be located in the room to the right of the golden door. One will be openly available to you, so you'll just need to use Lumos to attract it and bring it back to the golden door. For the other one, just destroy the spiderweb using Confringo or Incendio and then use Lumos to bring it to the door. It will then unlock, allowing you into the final room.
Defeat the Inferi inside here, and then you'll want to work on the puzzle in the middle of the room. From the treasure map you were given, you will need to flip over three of the stones on the ground using the spell Flipendo to correctly complete the puzzle. Face the opposite side of the entrance from which you came, and flip over the three stones shown above. You'll then receive your prize for successfully completing the quest.