Strangely or not, you’ll only find this dungeon, its wayshrine and the Erabenimsun Camp forge to the south of this area. Not including the volcano, this is probably the area with the lowest point of interest density in the expansion. Follow the road south from the Wayshrine, and you’ll end up straight at the entrance. If you speak with Neramo, who stands near the front door, you can accept the dungeon quest called “The Heart’s Desire”.
While inside, you need to find the central room, the one that has a lot of lava and the metal platforms. In this area, called Nchuleftingth Lavaworks, climb toward the southwestern platform. There will be a group of enemies close by. You’ll need to defeat them in order to grab the shard. They are persistent and will not back down.
The shard’s glow shows up only when you come really close. If you were to search for it while on the other side of the room, you’d have difficulty spotting it. The platform where it lies is a natural formation, not built like the other metal platforms.
Sand Kingdom Moons - Super Mario Odyssey Power Moons