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To the east of Stone Gate, on the exclamation marker shown in the picture above, you will find a small cave with some hilichurls inside. Clear them out and 3 treasure chests will appear.
North of Statue of the Seven - Geo
North of the Statue of the Seven - Geo in Stone Gate, there is a chest that is quite hidden in a box. Destroy the box to reveal it.
From the Wangshu Inn teleport waypoint, you can jump out the balcony and glide into the area next to the watermill. Go inside from under the area, and you will find a Cryo pillar that will give you a treasure chest when activated.
North east of Wangshu Inn, on a small separate island, you can find many small lion statues facing different directions. There is 1 empty spot in the circle of statues, fill it up with Geo main character's elemental skill and a treasure chest will appear.
Go to the top balcony in Wangshu Inn, and interact with the rockery basin there to get some dialogue.
Then go to the marked location in the mountain area that's just above Liyue Harbor.
You can start by going north from the closest teleport waypoint, then climb up from this location. You don't have to climb all the way up the mountain, but it is still quite a distance.
Near the middle of the two mountains, you will find a small area with a shovel. Interact with it and you will get a treasure.
North of Wangshu Inn, past the bridge, you can see some umbrellas near a tree. Walk around the tree and umbrellas and some slimes will show up. Defeat all of them and a hidden chest will appear.
Near the Water Wheel
When you teleport to Wangshu Inn, turn to the right, and jump off the fence and glide slowly. You can see a treasure chest shown in the picture above, as well as a treasure chest with some vines that you can see to the right of the picture.
Guyun Stone Forest
On the small island next to the teleport waypoint in Guyun Stone Forest, go to the marked location shown in the picture above, and you will find a boat on top of some rocks. Climb up to the top of the boat and destroy the rocks there to reveal a chest.
Crevice near domain
Near the domain door in Guyun Stone Forest, you to the spot shown above, and turn to the right to go inside a small crevice to find an easily missed treasure.
Near sleeping hilichurl
North east of the domain area, there is a hut with a sleeping hilichurl. Burn the wooden pikes in the hut, then clear the enemies and a hidden chest will appear.
Outside of the Ruins in Dunyu Ruins, shown on the marker above, you can stand on top of the dead branch and a hidden chest will appear.
There are 2 unlit pillars in Yaoguang Shoal that's somewhat hidden because it's underwater.
The one on the right, needs Hydro element. You can get closer to the pillar by using Geo element main character, then use charge attack with Barbara to activate it.
The one on the left requires fire, so you can use either Amber, or Xiangling's elemental skill to light it up.
Close to the Statue of The Seven in Mingyun Village, you can find a small hilichurl object that you can destroy. Some hilichurls will spawn 1 at a time after destroying them. Clearing them out will reward you with a chest.
North west of Mingyun Village, close to the beach area, there is a spot where you can burn the wood surrounding a circular platform. Some Pyro slimes will appear, and an Abyss Mage. Clear them out and a hidden chest will appear.
Burnable Wood 2
South west of the Statue of the Seven - Geo, in Mingyun Village, there is another spot with a pile of wood that you can burn. Once it's lit, a Pyro Abyss Mage will show up. Defeat him and a hidden chest will appear.