In the end, he acknowledges that even with his mighty "German will", he is no longer able to resist the powerful visions and auditory hallucinations, nor his madness-inspired impulse to depart his U-boat and enter the temple, now impossibly illuminated by what seems to be a flickering altar flame. Slipping on his diving suit, he releases his sealed manuscript in a bottle (which is later found on the coast of Yucatan), and goes willingly to his death.
In the end, he acknowledges that even with his strong will, he can no longer resist the visions and auditory hallucinations, nor his madness-driven urge to abandon his U-boat and enter the temple, now illuminated by a flickering altar flame. He slips into his diving suit, releases his sealed manuscript in a bottle (which is later found on the coast of Yucatan), and willingly faces his death.