Genshin Impact Palace in a Pool is a new one-time Domain on Watatsumi Island, but to enter it, you have to complete Genshin Impact’s Suigetsu pool puzzle first.
The Suigetsu pool puzzle involves a set of Electro totems and compasses.
That’s it for how to unlock Palace in a Pool in Genshin Impact.
There’s also a second step after the main puzzle that’s easy to miss unless you know where to look.