In order to unlock Enkanomiya, a new region in Genshin Impact, they need to clear first one of the several quests, "The Moon-Bathed Deep" World Quest, where they need to unlock every shrine in order to obtain the "Key of the Deep."
Enkanomiya, the underwater island that holds new gameplay mechanics and monsters that players would encounter, is one of the new additions made in Genshin Impact courtesy of its Version 2.4 Update. However, in order to gain access to it, they need to find the key sigils that are scattered across Watatsumi Island.