Iron Boots

Iron Boots are an item found in three of the seven 3D Zelda games.

Uses
Although they do not seem like a very intuitive item, they have a variety of uses throughout the games. They can be equipped to make Link extremely heavy, enabling Link to walk along lake bottoms, force his way through tough wind currents, hurt enemies and, exclusively in Twilight Princess, walk along walls and ceilings using magnetic forces.

Ocarina of Time
The Iron Boots can be found in the Ice Cavern near Zora's Fountain. Equipping Link with the Iron Boots, especially when repeating it over and over such as in the Water Temple, can be a tedious task for most players, forcing them to constantly pause the game to switch boots. When equipped, they make Link walk very slowly due to their extreme weight, but he can go at the bottom of lakes and other sources of water. Link must wear the Zora Tunic in order to stay underwater; otherwise, a timer will appear and, if he does not take off the boots and re-surface before time runs out, he will drown, and will result in a game over. They are required to traverse through the deep water in the Water Temple, and are also useful in the Shadow Temple, as they enable Link to walk against the fan currents and past some undead creatures without them noticing him. Link can use the boots outside of dungeons to explore deep water like that found in Zora's Fountain. In some cases, the young hero can find treasure, including a Piece of Heart.

In the 3DS version of Ocarina of Time, the Iron Boots have been changed from equipment to an item, thus making it so that switching them on and off requires simple tapping of the touchscreen.

The Wind Waker
The Iron Boots are also found in The Wind Waker inside a cave in the Ice Ring Isle. Although Link cannot wear them underwater, he can use the Iron Boots to avoid being influenced by the wind, making them required for the Wind Temple. They also allow him to activate a springboard by first wearing the boots and then taking them off. Additionally, wearing the Iron Boots and using the Hookshot on specific statues allows Link to pull the heavy objects down. Although the Iron Boots typically cause Link to sink to the bottom of water with them on, in this game, they will immediately un-equip when Link begins to swim.

The Iron Boots are an item assignable to X, Y, or Z, which made taking them on and off a lot easier than in Ocarina of Time.

Twilight Princess
The boots once again make an appearance in Twilight Princess. They are found in Mayor Bo's house in the Ordon Village after defeating him in a nice, friendly Sumo Match. Similar to The Wind Waker, they are an item assignable to specific buttons. They are used to ward off the Gorons on the way up Death Mountain, as well as the secret to defeating the Goron Elder, Gor Coron, granting access to the Goron Mines. They are also needed to defeat the confused Dangoro and Fyrus, the temple's boss and the Goron's patriarch originally called Darbus until being corrupted by the Fused Shadow.

The major difference between the Iron Boots in Twilight Princess compared to previous The Legend of Zelda games is that the Iron Boots are magnetic and allow Link to walk on roofs and walls that possess a certain material used in the Goron Mines. They are also required to complete the Lakebed Temple, and they allow Link to use Water Bombs while underwater. In the City in the Sky, they can be used similarly to the Iron Boots in The Wind Waker to hold Link steady in strong gusts of wind. Also, Link can roll with them on and hurt enemies, and become vital in the Fyrus, Morpheel, and Argorok battles.

Trivia

 * Although the Iron Boots do not appear in Majora's Mask, Zora Link has an ability identical to the boots' function: He can sink while swimming underwater in order to walk on the bottom.
 * There was going to be another set of boots in Wind Waker, called the Water Boots. They were supposedly a seperate version of the Iron Boots which'd allow Link to sink underwater like in Ocarina of Time, a test map indicates this. Problems like this came up considering the game takes place on an ocean, being a reasonable argument to cut the idea.
 * In reality, the Iron Boots would not be a good item for a temple filled with water, as iron is very easily corroded by water. Thus, the boots would quickly become rusty and useless.