First you need to get bombs, the Song of Storms,and the Boomerang. Then go to hyrule castle and jump in the moat so the guards won't see you. Drift until you see a shallow corner. Climb up and you will see a tree. Play the Song of Storms. A hole will open up, then jump down. There will be several walls that can be blown down with a bomb. One of these has a gold skulltilla behind it. BE CAREFUL, first kill the bug then stand right in front of the circle that sends you back to the surface. Next, throw the Boomerang at the token and as soon as it hit's the token step back on the circle. You will be back at the surface. If you did this right the gold skulltulla should still be there. Repeat this process until you have 100 or more.