One of the rifts can be found in Jabul Waters in northeastern Hyrule.

How to Go to Jabul Waters

From Lueburry's house, go west to Suthorn Prairie. Then go north to the northeast exit from Suthorn Prairie. You will arrive in Hyrule Field.

Hyrule Field

If you go near the soldiers, there will be a cutscene.

West of those soldiers, bind to the treasure chest and walk away from it to pull it out of the ground. Open it to get 5 jars of floral nectar.

Nearby, there is a Guay flying around. Defeat it and learn the Guay echo.

Go east to find a sign in the road. You should go east in the direction of Seesyde Village. Go north toward the water, and you find a stream with some fish monsters in it. You can switch to swordfighter form or use monster echoes to defeat the fish, then learn the Tangler echo.

Cross the bridge over this stream, then use bind on the nearby boulder and move it to reveal a Might Crystal.

East of that, there is a sign in the road. Go east from the sign.

There is a Crow on a tree, and a boulder next to the tree. Move that boulder to get another Might Crystal.

Go east from there to an area with a lot of boulders, as well as some Ropes and Caromadillos.

Keep following the path and you reach a new area with crab-like monsters walking around. Throw rocks at them and learn the Sand Crab echo.

Go east and check on the waypoint to add it to your map.

Go east from there to arrive at Jabul Waters. There will be a cutscene. This begins the quest The Jabul Waters Rift.