A chance to get a second, not-easily-broken sword as adult Link in The Legend of Zelda: Ocarina of Time presents itself when Link meets Biggoron, a giant Goron atop Death Mountain. Biggoron assures Link that his craftsmanship is much better than that of his brother, Medigoron - who will sell Link the Giant's Knife, which breaks after moderate use. Link then has a chance to repair a broken Biggoron Sword, provided he's gotten it from a the master craftsmen who is trying to repair the bridge in Gerudo Valley.
The broken Biggoron Sword is acquired through the first half of a trading quest, where Link trades various items with citizens of Hyrule like Dwight in the "Garage Sale" episode of The Office. This sort of quest is actually quite common in The Legend of Zelda, though it's usually used in the 2D games. These trading quests usually have a pretty lucrative reward, such as the pieces of heart earned in Majora's Mask, or are even required to finish the game, like learning the route through the Wind Fish's egg in Link's Awakening.
Ocarina of Time's trading quest, though, is the best in the entire Legend of Zelda series, because the Biggoron Sword is an incredibly good reward, while the quest itself is more engaging and challenging than its counterparts. It can also be completed early on by those are intimately familiar with Ocarina of Time. Acquiring Epona immediately after drawing the Master Sword from its pedestal, and buying Blue Fire from a shop in Kakariko Village, will allow players to get the Biggoron Sword before doing a single adult dungeon.
Ocarina's Trading Quest Reward Suits Its Difficulty
Many of the other trading quests in The Legend of Zelda aren't especially difficult. For instance, reaching the final boss in Link's Awakening requires that game's trading quest, but it can be done piecemeal leisurely throughout a playthrough. Many items in the Biggoron Sword quest have a time limit on them, making it a fairly difficult quest, especially if the player doesn't know exactly where they need to go. The quest also requires some preparation, like the aforementioned requirement of Epona, or the later necessity of making sure King Zora is thawed out. Players will also be able to do the quest easier if they planted the Magic Beans around Hyrule as kid Link.
Ocarina of Time's trading quest is also the best because of its reward - an item more powerful than the Master Sword that can be very helpful, but not required. The Biggoron Sword will deal twice as much damage as the Master Sword, but requires two hands, meaning Link has to sacrifice the protection of his shield. Getting the Biggoron Sword is a great way to add variety to The Legend of Zelda's gameplay, and can be used whenever players need to deal a lot of damage quickly. While it's not required to beat the game, the Biggoron Sword certainly makes it much easier.
There is a point in the fight against Ocarina of Time's Ganon where the Master Sword is knocked away from Link. The fight must be continued for a while without the Blade of Evil's Bane, usually with the Megaton Hammer in its place. The Biggoron Sword makes this part of the final battle trivial, even if it can't deliver the final blow once the Master Sword has been recovered. The added damage perks make obtaining the Biggoron Sword worth the challenge, and the engaging quest itself makes Ocarina of Time's trading sequence the best in the entire Legend of Zelda series.