Crescent Island is a volcanic isle in the eastern Fire Nation that once housed a temple for the Fire Sages and a shrine to AvatarRoku. Since the destruction of the island's sole landmark, the area has remained uninhabited.
Crescent Island is a volcanic island on the outskirts of the Fire Nation archipelago; the Fire Temple was the only structure on the island. The temple was built on the island so that it aligned with the solstices and equinoxes, and housed a branch of the Fire Sages.
After Avatar Roku destroyed the temple, the island became uninhabited. In fact, the lava still flows from that event. After his harrowing journey through a storm, Aang washed ashore the same crescent island where the temple once stood. The kids then began their journey into the Fire Nation from this tiny outlying island.
The Fire Temple was a five-tiered pagoda that sat on a hill near the volcano's base, managed by a small group of Fire Sages. Avatar Roku once called this temple his home, and it was here he perfected his use of the Avatar State; after his death, the temple was rededicated to him. The ancient temple used mechanisms that required firebending to operate. The temple was destroyed once by Avatar Roku in the Avatar State and again when Aang channeled his spirit to face the threat that was awaiting him at the Fire Temple, right after the winter solstice.
The sanctuary was built to receive a shaft of sunlight through a giant ruby at sundown on the winter solstice. The light illuminated the statue of Avatar Roku, making it possible to communicate with him. When Avatar Roku was alive, the previous generations of sages used the sanctuary to communicate with him on the solstice, but now only the Avatar is able to communicate with Avatar Roku. The sanctuary doors protected the sanctuary from intruders; they could only be opened by either a fully realized Avatar or with five simultaneous fire blasts.