The last of the eight major hells, the Great Avīci Hell, is also called the Hell of Incessant Suffering because sinners in this hell suffer interminable pain. It is located at the bottom of the realm of desire, beneath the Hell of Great Burning Heat. The length and breadth of the hell are 80,000 yojana each, and is surrounded by sevenfold iron castles. The extreme torment of this hell is beyond description except that it is 1,000 times as harsh as the sufferings of the seven major hells mentioned above or all the sufferings anywhere combined. The suffering is such that to sinners in this hell those sinners suffering in the Hell of Great Burning Heat appear as though they were heavenly beings playing in the Paranirmitavaśavartin Heaven. The stench from this hell would kill off all the heavenly and human beings on the four continents and six heavens in the realm of desire who smelled it. Only because two mountains called Shussen and Mossen block the stench of this hell from reaching the human world can human beings stay alive. If the Buddha were to preach on the torments of this hell in detail, humans listening to Him would die of agony, vomiting blood. This probably explains why the Buddha did not preach on this in detail.

The life span of sinners in this hell is one medium kalpa. Suppose the length of time equivalent to the period during which a man’s life span decreases by one in 100 years from infinite to ten years, and then increases from 10 to 80,000 at the same rate. The time required for this decrease and increase is called a small kalpa, twenty of which constitute a medium kalpa. Those who fall into this Hell of Incessant Suffering are subjected to the great torment of this worst hell for this long period of time.

Ken Hōbō-shō, A Clarificaton of Slandering the True Dharma, Writings of Nichiren Shōnin, Doctrine 3, Pages 111-112.