There once were brave souls who uncovered the truth of the Seventh Umbral Calamity. Such trials as they overcame were not to be recorded in history, but far from fading with the passage of time, they have been imagined in vivid detail by the wandering minstrel. As his lilting melody caresses your mind's eye, you cannot help but be transported to the scene of struggle against the elder primal Bahamut...
—Official description

The Unending Coil of Bahamut is a duty in Final Fantasy XIV. It is the first set of "Ultimate" difficulty content, intended to be of even higher difficulty than the existing "Extreme" and "Savage" difficulty levels. The duty comprises of a single encounter, where players first fight Twintania, Nael deus Darnus, and Bahamut Prime in succession, before fighting all three together. Once defeated, Bahamut Prime uses an unavoidable Teraflare to KO the party, which is then resurrected by the primal Phoenix to resume the battle against a stronger, golden version of Bahamut Prime.