Iron Boots

Iron Boots are an item found in three of the four 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 extremely useful in the game for getting through the Water Temple, although they are completely unnecessary for experienced players. They are also very useful in the Shadow Temple, as they enable Link to walk against the fan currents and past some undead creatures without them noticing him.

The Wind Waker
The Iron Boots are also found in The Wind Waker. 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. In The Wind Waker, the Iron Boots were 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.

Trivia

 * Although the Iron Boots don't 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.
 * The boots are also vital to defeat Argorok in Twilight Princess.