The Crescent Island Fire Temple was a five-tiered pagoda built atop a craggy hill on Crescent Island in the outer Fire Nation. It was maintained by the Fire Sages and 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.
The Fire Temple was originally founded on Crescent Island as a refuge for the Fire Sages, the Fire Nation's religious authority, on the outermost island of the Fire Nation archipelago. Its axis was built in such a way that the light of the sun on the solstices and equinoxes would penetrate the sanctuary and illuminate the eyes of Avatar Roku's statue.
In his quest to become a fully realized Avatar, Avatar Roku took shelter in this temple in 55 BG, where he eventually mastered the Avatar State. However, during the process, he partially destroyed the temple and was later forced to rebuild it. During the reconstruction, Avatar Roku carved a series of secret passages beneath the structure.
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 and illuminate Avatar Roku's statue, making it possible to communicate with him. 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.