The Lake Hylia Crystal
In-game Description
It seems that you can enter a Shrine of Light if you offer up a crystal.
Follow the ray of light, and offer up the crystal at the shrine.
Interactive Map Locations
45275. Hyrule Surface Map
X: 10159 Y: 13526
Found inside the 
Lake Hylia Whirlpool Cave, examine the Shrine to obtain it.
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