The Genshin Impact Nameless Treasure quest can net you a sizable bounty if you manage to complete the quest. Here's how you can find all the treasures and redeem them for rewards.
Genshin Impact Nameless Treasure: Dunyu Ruins
This treasure is hidden under water, so you'll need to lower the water level to reach it. First light all the torches in the ruins and then activate the Geo Element Node to lower the water. Next you'll need to find the three spirits roaming the newly explorable area. Once found the force field around the chest will lower allowing you to take the treasure.
For this treasure, you'll need to rescue an NPC who is being held hostage. Once you defeat the enemies around her, you can find a Treasure Hoarder's Key which you can use to free her. She'll then tell you the location of the Nameless Treasure.
There is a stone tablet in the center of the area that talks about five different seals to break. To do this find the five tower structure around the pool and use Geo to break each of the seals within. Once this is done the chest will spawn in front of the tablet.
Once you have found all the treasures you can redeem them with Linglang at Xigu antiques in Liyue Harbor next to the jewelry store. Keep in mind that Xigu antiques are only open at night past 9 pm, kind of like Kilton's shop in Breath of The Wild. You can sell the treasures to him for 100,000 Mora and 40 Primogems. You'll also get Adventure XP for completing the quest.