In Genshin Impact, Dreams Beneath the Searing Sand is the fourth and final quest in the Golden Slumber World Quest series, which takes place in and around Khaj-Nisut, in the Land of Lower Setekh, Great Red Sand, Sumeru. The quest starts automatically when you complete The Secret of Al-Ahmar.
Once you’ve passed the three trials around the outer part of Khaj-Nisut, make your way to the marker and operate the book-like device on the big fancy pedestal. Use the Four-leaf Sigils to get across to the massive new building that just appeared, then use the book-like device to open the biggest door yet. Go inside, have a chat, then drop down the hole on the left side. Operate the marked device then approach the central monument to start a puzzle.
How to activate the mechanism in the center of the hall
Release the floating cube on the west side, then follow it down the elevator. Get around the invisible walls on the left, then on the right, then touch the cube so that it lights up the large pedestal. Go back up to the main hall and release the cube on the south side. Follow it out of the hall and down a hole, then defeat a Primal Construct. Release the cube and follow it until it activates the fan at the far side of the room. Release it again from the same place, then follow it when the wall fans are off so that it reaches the floor fan and gets blown up to the main hall and lights up its large pedestal. Release the cube on the east side, and follow it to another Primal Construct. Defeat that, then release the cube again so that it lights up the large pedestal. Now you can operate each of the three devices in the hall, then touch the base of the central monument on its north side.
How to operate Prism of Khaj-Nisut
Use the fans to go up a few floors, then use the Four-Leaf Sigil to reach the highest platform. Switch it from red to blue, then use the Four-leaf Sigil to get to the blue device on the west wall (don’t panic, there’s an invisible floor). Start up the device, then activate the elevator to ride it up.
How to escape from Khaj-Nisut
Ride another elevator up, then approach the throne and, after a lot of conversation (and even some song and prayer), defeat Samail’s subordinates, oh which there are three waves. Next you’ll have to flee from the encroaching darkness. Run to the east, drop down the hole, then run west, go left then right around the invisible wall, and drop down another hole. Run east across the invisible floor then, after the first drop, run north, then further north after the second drop. Now run out of the exit on the west side to escape Khaj-Nisut.