Secret Golden Skulltulla at Lake Hylia
First off, you need to have beaten the Water Temple. Warp to Lake Hylia, whether you are there or not, and look at the tree. Get out your Longshot and just at the little arrow there just above the limb, shoot it. Make sure that you're looking at the right tree, the one you need to go to is the one with the claw marks. You will go up and land on an out stretched limb. Play the Suns Song and turn to where the very top of the tree is. There will be a Gold Skulltulla if it is night. Use your Longshot and kill it and collect the token. Also, the reasons that you need to beat the Water Temple is because...
1. You need the Longshot
2. You need to be able to see the sun and moon