Changlong Island, prison.
This prison, built deep underground on Changlong Island, is shrouded in perpetual darkness, created by the Sea Dwarves through a millennium of toil.
It is said that all natural energies of heaven and earth are cut off within the prison, and it is exceedingly durable. Even prisoners at the peak of the Heaven Venerate Realm are unable to forcibly break out.
Moreover...
Within the prison, only a very small amount of food is provided each day.
Unable to replenish their energies with the natural essence from the outside world and constantly needing to use their own energy to resist the prison's chilling environment, this scant amount of food becomes a treasure of inestimable value.
To survive, prisoners numbering tens of thousands would fight and kill each other like bloodthirsty demons whenever food is distributed.
It's akin to purgatory on earth.
