Journeying through Hyrule in Ocarina of Time sometimes requires some pretty heavy offense or defense, and Link's base items and power are often not quite enough to take down the strongest of enemies or puzzles. He'll have to find certain ways to power up his arsenal to overcome the challenges standing between himself and saving the kingdom.
Luckily, the mysterious and powerful Great Fairies are around to give Link some real boons. They can be found in a variety of places, each time offering a new item, ability, or power that will help Link on his way. Here are all the places you can find the Great Fairies and what each provides Link with.
6 Death Mountain Trail
Looming over Kakariko Village is the foreboding and treacherous Death Mountain, which can be accessed via the Death Mountain Trail. Along this dangerous path you'll find enemies, falling rocks, and a secret cave where the Great Fairy of Power can be found. You'll need to be playing as Child Link to find this secret Fountain.
When you see a red flag along the trail, head left. You'll need some bombs or bombchus to blow up some rocks that you see across the gap. It takes some finicking with the timing, but once you get it, you can continue ascending the mountainside. The Great Fairy can be found inside a bombable cracked wall at the summit, where she'll give Link the magic meter and upgrade his spin attack.
5 Hyrule Castle
As Child Link again, you can head to Hyrule Castle to begin looking for this Great Fairy Fountain. Get past the guard and then go right at the fork in the path. There'll be a rock here that you can remove with the help of some bombs. As always, there's a pedestal where Zelda's lullaby can be played with your ocarina.
Once the Great Fairy of Magic appears, she'll grant Link a new item: Din's Fire. This new spell allows you to create a fiery blast at the cost of some magic, which can help take down multiple enemies and even open the gate in the Shadow Temple. This makes it the only one of the three spells that is actually necessary to finish the game.
4 Zora's Fountain
Another of the spells that can be obtained is Farore's Wind, a green spell that allows Link to warp within dungeons. First, place the warp point by using the spell, then return to it at any point by using the spell again. It's a very useful spell that allows you to return to certain areas of a dungeon without repeating the same rooms multiple times.
To obtain this extremely useful item, head to Zora's Fountain as either Child or Adult Link and enter the area where Lord Jabu Jabu resides. Behind a bombable wall in the southeast section of the area, a Great Fairy Fountain can be found. Play Zelda's Lullaby and the Great Fairy of Magic will appear again, granting you the item.
3 Death Mountain Crater
If you're playing as Adult Link and have obtained the Megaton Hammer, you'll be able to access the Great Fairy Fountain in Death Mountain Crater. After heading into the Crater via Darunia's throne room, you can see two rocks to the right.
Smash them with the Hammer and you'll find yourself in the Great Fairy Fountain. After playing Zelda's Lullaby, you'll be greeted by the Great Fairy of Wisdom, who will proceed to double your magic meter.
2 Desert Colossus
The Great Fairy of Magic, who has previously granted you Farore's Wind and Din's Fire, can be found a third time pretty late in the game (earlier if you do the Spirit Temple before the Shadow Temple). Once you have access to the Spirit Temple as Adult Link, you can find a cracked wall near the entrance by some trees. As always, use the bombs to open this cave and enter, where you'll find the prescribed Zelda's Lullaby pedestal.
This will provide Link with an appearance from the Great Fairy of Magic, who gives you the third and final spell, Nayru's Love. This item allows Link to create an almost impervious barrier around him at the cost of magic, making him basically invincible to most attacks and enemies for a short time. Beware, though, as it won't make you completely impervious to Ganon's attacks, but it will lessen their strength.
1 Ganon's Castle
Speaking of Ganon — you'll need quite a bit of health if you hope to take him on, and the Great Fairy of Courage is here to help. Just outside of Ganon's Castle toward the end of the game, Link can find a Great Fairy Fountain hidden by a giant pillar. Use the Golden Gauntlets to remove this pillar, and enter the Fountain.
Here, the Great Fairy of Power will grant Link with a major defensive boost, basically causing him to take half damage from all attacks, effectively doubling his overall health.