The Lost Valley Domain
The Lost Valley is a Domain that was added to Genshin Impact with The Chasm area in Update 2.6! The Domain is initially sealed and you will have to complete a simple puzzle to unlock it. The Lost Valley is located North of the area’s Statue of the Seven. There is a group of enemies guarding a common chest in front of the sealed entrance. Defeat the enemies and loot the chest first.

To unseal the entrance you will have to interact with the minerals formations nearby. A Geo character that can create Geo constructs is necessary. Zhongli or Geo Traveller are an example.

Go near the resonating mineral formation and place a Geo Construct to create a shockwave. The shockwave will travel to the other mineral formations nearby but it cannot reach the entrance by itself.

To help it travel farther and unseal the entrance, place a second Geo construct between the entrance and the nearest mineral formation. The shockwave will now reach and unseal the entrance. Follow the path inside to find the Domain. Before you enter The Lost Valley, jump down and explore the cavern to discover a Luxurious chest.

Domain Info
The Domain offers two Artifact Sets, the Echoes of an Offering and Vermillion Hereafter.
Echoes of an Offering boosts ATK by 18% and when Normal Attacks hit opponents, there is a 36% chance that it will trigger Valley Rite, which will increase Normal Attack DMG by 70% of ATK. This effect will be dispelled 0.05s after a Normal Attack deals DMG. If a Normal Attack fails to trigger Valley Rite, the odds of it triggering the next time will increase by 20%. This trigger can occur once every 0.2s.
Vermillion Hereafter boosts ATK by 18% and after using an Elemental Burst, this character will gain the Nascent Light effect, increasing their ATK by 8% for 16s. When the character’s HP decreases, their ATK will further increase by 10%. This increase can occur this way a maximum of 4 times. This effect can be triggered once every 0.8s. Nascent Light will be dispelled when the character leaves the field. If an Elemental Burst is used again during the duration of Nascent Light, the original Nascent Light will be dispelled.
To complete the domain the elements of Pyro, Electro, Geo and Anemo are recommended. The enemies you will face are machines.