A large rift appears at Holy Mount Lanayru, so you go north to investigate.

How to Reach Holy Mount Lanayru

To reach Holy Mount Lanayru, go to the southern gate of Hyrule Castle Town and go clockwise around the castle wall until you reach the bridge to the west. Cross it, then go west to where there are some ruins, and stairs leading down. Go down the stairs and go to the left to get a Might Crystal. You can optionally go south into the water and dive into the hole to reach the Royal-Family Shortcut.

Exit the underground area and go east to the dirt path, then go north. When you reach the sign in the road, keep going north. When you reach the fork in the road, you can talk to the Smoothie Shop owner to add this shop location to your map.

You can optionally go to the rift east of the Smoothie Shop. There is a glowing spot on it, so you can check on it to have Tri make an entrance, then check on the entrance to go to the Stilled Northern Sanctuary.

Go north on the dirt road and follow the path. You find a soldier and a person north of the soldier. Talk to them for some clues about how to proceed. Go north to find a blocked cave entrance. Create a Bombfish echo in front of the blocked door to break it open.