Water Temple (Ocarina of Time)

Deep under the vast Lake Hylia lies an ancient temple known as the Water Temple. It requires the use of the Iron Boots to get to its entrance gate and the Hookshot to simply open it by shooting the target above. In various parts of the Temple, it is required to go underwater for substantial amounts of time, thus necessitating the Zora Tunic (though the Water Temple can be beaten without it by an experienced and resourceful player). Its enigmatic structure consists of various levels and requires the use of playing Zelda's Lullaby to each of the Lion-type markings on the walls. You will need to use all your intellectual skills and cunning surviving techniques to truly conquer this temple. This will be hardest temple you have come across yet and possibly the hardest in the entire game. Be very aware of your surroundings since you never know what to really expect. You shall also come to confront your very own shadow-self sometime while progressing your way forward. Once you acquire the Longshot, you can get the boss key and get to the aquatic boss, Morpha.

Minor Enemies and Traps
Blue Tektite, Shell Blade, Stinger, Spike, sink holes, whirlpools, spikes

Trivia

 * The Water Temple was made completely as a tribute to Lord Jabu-Jabu.
 * Due to the frustrating swimming mechanics and the incredible length, many regard the water temple as the most "annoying" dungeon in OOT, and some, the most difficult Zelda dungeon yet.
 * It is very likely that the Water Temple and the Lakebed Temple of Twilight Princess are the one and same location.