Gate of Time

The Gates of Time are a pair of gates that appear in SS undefined. Each gate is capable of creating a portal through time to travel to the era just after Hylia's fight with Demise. The Gate of Time located in the Temple of Time was constructed by the goddess Hylia.

Features
The Gate of Time looks like a giant gear being spun by two smaller gears in either upper corner. It has 12 teeth and a symbol on each tooth, bearing resemblance to the hour indicators on a clock. The Triforce can be seen in the center of the gear surrounded by the symbols of Din, Nayru and Farore and what appears to be musical notation. When the gate is touched, a spiral of hollow, blue gear shapes appear to indicate that it is open, and the original glassy surface reappears when it is closed.

History
The first Gate of Time Link encounters is in the Temple of Time in the Lanayru Desert. Impa and Zelda are about to enter its threshold when Ghirahim appears and attacks. Link intervenes after Impa is overwhelmed by Ghirahim's power and Zelda entrusts the Goddess's Harp to him just before they both escape, destroying the Gate of Time behind them.

Link travels to the Sealed Grounds where the old woman reveals the existence of a second Gate of Time. Ghirahim learns about the second Gate of Time from a drawing in the Fire Sanctuary. To activate it, Link must temper the Goddess Sword into the Master Sword by obtaining the three Sacred Flames hidden in the Faron, Eldin, and Lanayru provinces. Eventually Link is successful in this endeavor, though his efforts necessitate resealing The Imprisoned on multiple occasions, and meets Zelda in the distant past. After she enters a deep slumber, Link uses the gate again to return to the future and quest after the Triforce. He uses the gate during this mission to plant the Life Tree Seedling in the past and recover the Life Tree Fruit in the present to revive Lanayru.

After Link wishes upon the Triforce for the destruction of Demise in the present, Ghirahim abducts Zelda and takes her through the gate in an attempt to revive Demise in the past. Link and Groose follow through the gate to rescue Zelda, and after they succeed, they use the gate a final time to return to the future.

Theory
It is likely that the Gates of Time were composed of Timeshift Stones. When Link reactivates the Gate in the Sealed Temple, it first splinters into a series of cubic structures, which are covered in markings similar to those seen on Timeshift Stones and seem to glow with a similarly-colored light. These structures are then shown to rotate and fit together in a very specific manner, perhaps as a way to redirect and focus the otherwise mostly-unconstrained Timeshift fields. This might be what allowed the Gates to open concentrated portals through time, as opposed to transporting everything in a given radius back through time.

Trivia

 * The pattern on the gate can be seen on the game's box art. On the boxart, the words "Wisdom", "Nehru", "Power", "Din" and "-rol" can be seen written in Hylian. This text has been removed from active Gates of Time, but can be faintly seen on the broken gate in the Temple of Time.
 * In Japanese both the Door of Time and the Gate of Time share the same name,.
 * The Gates of Time behave in a way nearly identical to theoretical structures known as wormholes, which are believed to allow instantaneous travel across vast regions of space and/or travel through time by passing through holes in the fabric of the universe. It is possible that the idea of wormholes may have inspired the Gates of Time.
 * Upon being activated, the Gates of Time somewhat resemble the Mirror of Twilight.
 * At one point in, Link must walk through a special door in order to be transported into the past and enter the Temple of Time, and must then go through the same door to return to the present, thus making the door virtually identical in function to the Gates of Time.