1. Locate the entrance - Open the map and head towards the lower right corner of Mondstadt to find the location of Oath Gap.
2. Guide the fairies - Near Oath Gorge, you need to guide three fairies to the three designated points, and be careful to clear out any enemies you may encounter along the way.
3. Use the wind field - After successful guidance, pass through the wind field area in the middle and step into the purple teleportation circle. Once the first teleportation is successful, subsequent teleportation points can be passed through any of the teleportation points in the illustration.
• Go to Oath Point and look for the suspended portal entrance.
• Defeat the monsters in Oath Point and find and activate three little fairies, which will activate nearby mechanisms.
• Follow the guidance of the air flow and enter the mysterious world - Musk Reef through the opened portal.
• On Mask Reef, you'll see a gorgeous treasure chest. Next, just activate the nearby wind element trap.
• When the mechanism is activated, three slimes will appear. After defeating them, the puzzle of the treasure chest will be solved and the treasure chest will be opened.
Now that you have the detailed steps to get to Mask Reef and unlock the treasure chest, I wish you a fruitful adventure!