User blog comment:IamJakuhoRaikoben/Chapter 348: Return of the Demon, Review./@comment-5840892-20130824192632/@comment-7418318-20130825234410

As for what it means, maybe he was literal and somewhere close-by is the entrance to some place called the underworld. But since he said "in this world is a place called the underworld" I guess he might be refering to a cave system or somesuch instead of a metaphysical place like Hell.

Or there might be a portal to a hellish parallel world.

Either way I think Tartaros have their Headquaters and the majority of their members there.

And further I could be that the intent of the freezing spell was to close that entrance/portal/whatever to the underworld, but either the caster miscalculated or there was some magical interference that caused the spell to grow out of all proportions and encase the village as well.

If it really is an Iced Shell derivate, closeing off the underworld could provide the necessary motivation for some individual or maybe even a group of people to sacrifice their own lifes.