If you explore east of Devantaka Mountain, you'll find an Eremite camp with an Energy Extraction Device that can be diffused with the help of Control Keys. Reference the image below to find the exact location of the Challenge. Since the area is swarming with enemy Eremites, make sure to bring a battle-ready team.
Once you get there, you'll find a mechanism called an Energy Extraction Device. Approach it to begin a Challenge where you must find two Control Keys to deactivate the Device.
How to Look for a way to control the extractor in Genshin Impact
In this part, you need to find the two missing Control Keys in order to shut down the Energy Extraction Device. You can obtain them in any order.
First Control Key location
Climb the ladders to the top of the building, where you'll find a huge crack in the wall. Enter the crack to find the first Control Key. Approach it to claim the Key—no need to defeat the Eremites.
Second Control Key location
Jump down until you see the entrance pictured above. Enter it to find the second Control Key. There's a Dendro boulder and an Auspicious Branch inside, but interacting with them will only summon more Eremites, so you can leave after approaching the Key.
How to guard the extractor until it shuts down in Genshin Impact
After obtaining the two Control Keys, interact with the Energy Extractor Device at the top of the building to begin a battle segment. A circular gauge will appear above it. Your goal is to stand beside the Device until the gauge above it becomes full. If you're too far away or if there are enemy disruptions, the gauge will stop filling up, so make sure to defeat all the enemies that spawn and stand close to the Device afterward. Once the gauge is all filled up, the Energy Extraction Device will turn off, rewarding you with an Exquisite Chest.
Check out our guide on How to solve the Energy Extraction Device Challenge south of the Ruins of Dahri in Genshin Impact to complete a similar Challenge in Sumeru.