Once you use the lever to set the lift in motion, it’s going to take you to Blackreach: Greymoor Caverns and its western part, right at the Dark Moon Grotto great lift. The Dark Moon Grotto mentioned in the title is a place of interest that’s, of course, a cave. It is placed at the center of this part of the map. From the Dark Moon Grotto great lift, head south all the way down. You’ll pass by the Dark Moon Grotto and its Wayshrine, and eventually reach its southernmost part where you can discover the Grotto Falls Wayshrine and the Colossus Charging Station world boss.
From the Grotto Falls Wayshrine, look to the southwest, and you’ll spot some stone structures. Go between the large boulder and a mushroom cap, and soon enough you’ll go down a small hill. A little plateau will take you underneath a larger platform, also made of stone. At this point, you should notice the beacon light from the shard we are after. It is just between the cave wall on the south, and a small pond on the north, just below the stone stairs that lead to the platform above.