Great Bay Temple

The Great Bay Temple is the third dungeon in Majora's Mask.

Entrance to the Temple
The dungeon can be seen far away from Great Bay Coast and Zora Cape. At the time the events of the game begin, the temple is victim of a curse that leaves the sea of Great Bay murky. Once Link recovers the Zora Eggs laid by Lulu and takes them to the Marine Research Laboratory, Link learns the New Wave Bossa Nova, a melody he must play while in Zora form to summon a turtle just outside the back entrance of Zora Hall so that the turtle can take him to the temple.

Themes and Navigation
To progress within it, Link needs to open numerous valves that are part of an extremely complex network of pipes. Doing so enables the functionality of water-based elevators that help Link reach new places. Eventually, he has to invert the direction of the water's continuous flow so that the flux can take him to new parts of the temple.

The key item in this dungeon is the Ice Arrow, which Link can acquire after defeating the mini-boss Wart. At this point in this temple, it possible to skip the rest of it and move on to Ikana Canyon (Link will need to return to finish the temple later, though). He later uses Ice Arrows to defeat the Mad Jelly and Gekko for the Boss Key. The Ice Arrows are also essential to navigate certain areas by means of freezing the surface of deep water and even some enemies for use as platforms, which can be used to reach valves that would be otherwise inaccessible.

If Link is able to collect all 15 stray fairies in the dungeon and return them to the Great Fairy Fountain, his reward is a Defense upgrade. The Boss of this Temple is the Gargantuan Masked Fish: Gyorg. After his defeat Link receives a full Heart Container and Gyorg's Remains.

As an indication that Termina is more technologically advanced than Hyrule, the Great Bay Temple is actually one big factory, with churning gears, rooms and passages illuminated by neon lights (which suggest that part of the energy provided by the water motion is turned into electric energy to ensure the operability of all the machinery), and the previously cited water-based elevators and valves. Link has to activate the yellow-colored elevator to gain access to most of the temple itself, the red-colored elevator to gain access to the rotating lever that helps Link to invert the water's flow direction, and the green-colored elevator to gain access to the entrance to the boss's lair.

Trivia

 * As stated before, the Great Bay Temple is a perfect example of Termina's technological advances. No one knows for sure just how the Zoras overcame such engineering feats. Both Termina and Hyrule share advances in technology so ancient that none of the current inhabitants can tell of their origins. However, most technology within the Zelda series seems to be centered around wind, water, and earth powered machinery.
 * There is a glitch that allows Link to reach the dungeon with Ice Arrows only. Using said glitch, up close the Great Bay Temple appears to be shaped like a fish.
 * The water where Gyorg swims cannot be frozen with the Ice Arrows.
 * Great Bay Temple, as with the Water Temple and Lakebed Temple, is notably complex and difficult (not to mention lengthy) in comparison to the other dungeons of Majora's Mask.