If you are outdoors in Imperial City, go to the Arboretum District. You’ll find the Irrigation Tunnels sewer entrance in the northeastern section of this part of town. There is a small room that hides the circular sewer doors. Use it to reach the part of the tunnels closest to the shard.
Once you’re in the Irrigation Tunnels, head to the Drain-Dweller’s Outpost area of interest. Enter the circular room south from this POI, and go east. Be careful with the enemies in the next room, on the ground level, just behind the wooden wall. They are not that strong, but if you don’t want unnecessary fights, you can avoid them. This doesn’t include the crocodiles defending the crystal. They come in groups of two, and are not easy to defeat. Maybe this one got its name from the fact they always respawn, no matter how many times you kill them.
Sand Kingdom Moons - Super Mario Odyssey Power Moons