The Millenio Sandbar is found within Lanayru Wetlands. It contains areas of shallow water, with small pieces of land and trees all around. In the center of the sandbar, there are several larger islands that are interconnected with small wooden bridges.
Nearby Korok Seeds
Climb the tree and pick up the rock.
Remove the large rock using Stasis, then pick up the smaller rock.
Catch the fairy lights.
One tree has too many apples, remove some until it matches the other two.