Fire Temple

The Fire Temple was a five-tiered pagoda that sat atop a craggy hill on Crescent Island in the outer Fire Nation. It was managed by the Fire Sages, and was closely associated with Avatar Roku, who studied there for many years to master the Avatar State. The ancient temple used mechanisms that required Firebending to operate; for example, the sanctuary door could only be opened by five simultaneous fire blasts.

History
The Fire Temple was originally founded as a refuge for the Fire Sages, the Fire Nation's religious authority, on the outermost island of the Fire Nation archipelago. Its location, on the volcanic Crescent Island, was chosen for its strong connection to the element of Fire.

During his Firebending training, Avatar Roku lived for a while at this temple, and it was here he perfected his use of the Avatar State. However, during the process he destroyed the temple, and so was later forced to rebuild it. During the reconstruction, he carved secret passages in the rock under the temple.

The temple was destroyed during the events of Winter Solstice Part 2: Avatar Roku.

In The Awakening, during the storm, after Aang creates a huge tidal wave with Yue's help, he got washed up on the Crescent Island, where the Fire Temple once stood.

Sanctuary
The sanctuary was built to receive a shaft of sunlight through a giant ruby and cast a spot of light within the sanctuary. At sundown on the winter solstice the spot of sunlight would reach Avatar Roku's statue. The light would illuminate the statue, making it possible to communicate with Roku. When Avatar Roku was alive, the Fire Sages used the sanctuary to communicate with him on the solstice, but after his demise, only Aang was able to communicate with Avatar Roku. The sanctuary's massive door protected the sanctuary from intruders. These doors could only be opened by either a fully realized Avatar or with five simultaneous fire blasts.

Trivia

 * Avatar Roku destroyed the temple twice - using the Avatar State both times.
 * Aang may have demostrated his status as a fully realized Avatar in the series finale, during his battle with Phoenix King Ozai . He produces five massive blasts of fire (one from each arm, each legs and from his mouth), whether or not this is how an Avatar might open the Sanctuary is unknown.
 * The design for the Fire Temple was based on Yellow Crane Tower in Wuhan, China.