Inside the Deku Tree

Inside the Deku Tree is the first dungeon in The Legend of Zelda: Ocarina of Time, and therefore the first 3D dungeon in the Legend of Zelda series.

Story
Prior to the events of The Legend of Zelda: Ocarina of Time, Ganondorf cast a 'death curse' upon the Great Deku Tree in order to force him to relinquish the Kokiri Emerald. Realizing that he could not survive the curse, the tree sent his assistant Navi, a blue fairy, to find Link, knowing that only Link had the courage to challenge Ganondorf and that it was time for Link to discover his destiny. Navi located Link and became his partner, but Mido refused to grant Link access to the Deku Tree's meadow, jealous of the favoritism shown towards Link. After collecting a sword and shield, Link was finally allowed to reach the tree, who explained his plight. However, he neglected to mention that he was already doomed to die from the curse. After asking Link whether he was courageous enough to help, the tree opened his mouth and allowed him to enter the dungeon, which would stand as a test of his bravery.

After defeating Queen Gohma, the parasite which had been infecting the tree, Link was warped back to the meadow and rewarded with the Kokiri emerald that Ganondorf had wanted. The Deku Tree finally explained that he would soon die, despite declaring that Link had been successful. He also told Link that he must leave the forest, venture to Hyrule Castle, and find Princess Zelda.

Dungeon
The first half of the dungeon takes place in the trunk of the Deku Tree. Here Link fights Skullwalltulas and Deku Babas in the "main room", and enters smaller side-rooms to find the Compass, Dungeon Map, and Fairy Slingshot. Business Scrubs can also been found here.

The second area is only accessible through a web in the floor of the first room. Link climbs to the top of the trunk and jumps from a ledge with his sword out in front of him. He slices through the web covering a hole at the base of the trunk, leading to the roots. This area is heavily water-logged and contains a platform unreachable at this time. It is here that the second part of the dungeon begins. Link fights more enemies and solves more puzzles, including destroying webs with burning Deku Sticks and shooting Eye Switches with his new slingshot.

He finally re-emerges into the main root room from a different entrance, and is now on top of the highest platform. This allows him to use another burning stick to break another web, which drops him next to the boss room. Here he is challenged by the three Deku Scrub Brothers. They can only be beaten if they are attacked in a certain order, but fortunately Link had happened across a fourth brother earlier in the dungeon who had told him of this. After he beats them in the order 2-3-1, they reveal the secret weakness of their master, Queen Gohma, and Link is able to enter the boss' chamber.

Items

 * Fairy Slingshot
 * Heart Container
 * Kokiri's Emerald

Enemies
Note: this list is based on the original version of The Legend of Zelda: Ocarina of Time rather than The Legend of Zelda: Ocarina of Time Master Quest.
 * Deku Baba
 * Deku Scrub
 * Gohma Larva
 * Gold Skulltula
 * Skulltula
 * Skullwalltula

Mini-bosses

 * Deku Scrub Brothers

Boss

 * Queen Gohma

Trivia

 * This dungeon continues a trend in Zelda games of the first dungeon being forest themed. It is also the second dungeon to take place in a tree, the first being Level 1 of The Legend of Zelda. However, that dungeon was presumably a dead tree, so this dungeon is the first to take place in a living being.
 * Also, the code to open the final door, 2-3-1, is most likely a reference to a code that was used once or twice in earlier Nintendo games, notably in Super Mario 64, in the Boo's Mansion level, in the mission when Mario runs through the library to find a star, and opens the door to the star by pushing in books in order 2-3-1.