Moulder of Mountains is an Archon Quest relating to Liyue in Genshin Impact.
Your task is to seek out the adeptus Mountain Shaper to tell him about the murder of Rex Lapis.
Here’s a walkthrough of Moulder of Mountains in Genshin Impact.
Go to Mt. Hulao
The adeptus is located at the peak of Mt. Hulao. If you’ve unlocked the area, you can use the waypoint there.
Otherwise, Mt. Hulao is on the left side of the map.
As you reach the area, you will see the adeptus’ abode. Talk to the treasure hoarder in the area.
Look for his brother in the amber
The treasure hoarder will tell you that his brother is trapped in one of the ambers.
The ambers are like glowing orange crystals you see all around the mountain.
Use a character with a heavy weapon (claymore) to destroy these ambers easily.
To find the person, just follow the path down from the top.
The exact amber which led to the discovery of the brother is shown in the image below.
Edited: Apparently the amber can be located elsewhere for other players.
Return to the brothers
Go back to the peak and talk to Li Ding and Li Dang.
After the brothers left, you’ll be introduced to Mountain Shaper who is furious that you set the thief free.
Talk to Mountain Shaper
Speak with Mountain Shaper to explain what really happened in Liyue Harbor.
The quest ends here.