Ganon's Castle
Time stands still at Ganon's Castle, and it stays the same whatever the time of day. There is only one Gold Skulltula to be found here.
Since he has taken control of the Triforce, Ganondorf Dragmire has transformed Hyrule Castle into his own. The once beautiful grounds of the castle are now a wasteland; Ganon's own castle now hovers above a pool of lava, with no way to reach the other side.
GAINING ACCESS
You will only be able to venture into Ganon's Castle once you have all of the Sages' Medallions and the Light Arrows. That done, go to the edge of the lava pit with a small series of steps. Rauru will tell you about the energy barrier which protects the castle's inner keep, and that you must destroy each of the cores before you can face the final battle. The six Sages will then create a rainbow bridge for you to cross, and you will have access to Inside Ganon's Castle.
GREAT FAIRY FOUNTAIN
If you go past the stone arch and explore more of the grounds, you will find a pillar with the Emblem of Time on it. If you have the Golden Gauntlets, you will be able to lift this pillar and reveal the entrance to the Great Fairy of Courage's fountain. Play Zelda's Lullaby on the Triforce symbol, and your Life Meter will be encased in white instead of black, signifying it will deplete at half the normal rate in future.