Jahannam (イアハンナン Iahan'nan) was a lost, isolated city said to be located exactly beneath the city of Altum. According to recordings, Jahannam was a sunken island trapped in the underground of Nihil, believed to lie beneath the earth or at its farthest reaches due to ancient volcanic eruptions. The city's remainings were then eventually known as the prison and supposed grave of the malevolent entity called The Opposer. Due to its status as being stuck on the underground, it was composed primarily of rock and ice, bringing unfavorable conditions for living beings and making its access theoretically impossible.

The time of Harthatenarl's imprisonment is named The Time of Peace.

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