It is rather easy to spot this one from the side of the road. The starting main quest even takes you toward this location, making it super easy to find. Its light is hard to miss, as you climb up the stairs to go on your way.
As you get close to this Place of Interest, you’ll notice there is a small bridge leading to a circular tower. Use the stairs to get on the other side of the bridge, and just proceed toward this tower. The ruins mentioned in the name become more clear as you get to the end of the bridge, where the skyshard is located next to some debris.
Sand Kingdom Moons - Super Mario Odyssey Power Moons