After you and Tri seal the rift in eastern Gerudo Desert, you get permission to drain the Sanctum of sand by going into the Cryptic Cavern.
Find the Seal
Turn to face the glowing object with an eye on it, then create a flying tile and wait for the tile to hit the object. The eye will close and the door will open. Go through.
Go to the southernmost Wind Cannon and bind to it, then move it over the pit and release it. Then create a boulder in front of the second Wind Cannon to block the air. Then go north and through the door.
Create a Darknut echo to attack the spinning metal things. When you defeat one, check on it to learn the Pathblade echo. Go north, but don't try to go past the four Pathblades. Instead, create a Pathblade of your own to hit the glowing thing with an eye on it. You will need to wait for the Pathblades to stop before you create yours so that your Pathblade won't get destroyed by the others.
After you close the eye on the glowing object, go east. There are a couple of mummies walking around. Create an Ignizol to burn the mummies. They will run around on fire for a while, then will be defeated. Check on the shimmering monster form that they drop, and you can learn the Gibdo echo.
Open the chest where the Gibdos were, and you find a Small Key.
Then create a Wind Cannon echo to blow away the sand in the corner. You find 5 rupees.
Go southeast and then south through the door. There are Arurodas here. Defeat them to make the western door open. Before you go, create a Wind Cannon and blow away the sand to find 20 rupees. Then go through the west door.
Walk in front of the Wind Cannon to be pushed south. Then go to the west wall, then go north and unlock the door, then go through. Go down the ladder.
Go to the left, then go down the ladder. There is a Pathblade beneath you. While holding onto the ladder, you can create a monster echo to destroy the Pathblade. Then go to the right, where the Pathblade was. Use an echo to go over the raised floor, then go to the right and go down the ladder.
Bind to the Pathblade and pull it over the gap, and release it so it falls down below. Then jump over the gap on the left, and pick up and throw the pot to find a fairy.
Go to the right and drop a boulder on the Pathblade that you dropped below. Then go down and drop a boulder on the next Pathblade below. Fall down where the boulder went, then make table with a Decorative Shrub on top to block the Wind Cannon. Then make a Strandtula next to that, and climb up the silk and try to jump from there to the ledge with the treasure chest. Walk in front of the treasure chest and open it to get 20 rupees.
Then go to the right and through the passageway to reach the next room.
Create a Strandtula to climb up to the second ledge. Then use a Wind Cannon to blow away the sand on this ledge. Then when the Pathblade is moving back toward the right, go down to the same level as the Pathblade, and create a Flying Tile. It will destroy the Pathblade.
Go up the ladder and stand on top of the ladder without going to the left. Then create a Pathblade, and quickly create a Wind Cannon on top of the Pathblade. When the Pathblade goes to the left, your Wind Cannon should get rid of the pile of sand. The enemy Pathblade will fall down below, so you can just make a Flying Tile to take you to the ladder on the left. Go up.
Before you go to the right, go left and step on the button to open the door. This gives you a shortcut.
Go back to the right, and you find a mummy with black wrappings. Don't use fire on it, or it will turn into a ReDead. Instead, create Pathblades to the left and right of it, and wait for the Pathblades to defeat it. Then you can learn the Gibdo Lv. 2 echo.
Then go through the passageway on the right.
Go to the right and press X to bind to the stopper that is blocking the sand above it. Move to the left to pull on it until it moves to the left, allowing the sand to fall. Then you can go to the left and go up the ladder, then go south until you're outside. Then you can go east and go through the door.
Go north and check on the glowing spot in the rift, then after Tri opens it, go in to enter the Gerudo Sanctum.