Our Lady showed us a great sea of fire which seemed to be under the
earth. Plunged in this fire were demons and souls in human form, like
transparent burning embers, all blackened or burnished bronze, floating
about in the conflagration, now raised into the air by the flames that
issued from within themselves together with great clouds of smoke, now
falling back on every side like sparks in a huge fire, without weight or
equilibrium, and amid shrieks and groans of pain and despair, which
horrified us and made us tremble with fear. The demons could be
distinguished by their terrifying and repellent likeness to frightful and
unknown animals, all black and transparent. This vision lasted but an
instant. How can we ever be grateful enough to our kind heavenly Mother,
who had already prepared us by promising, in the first Apparition, to take
us to heaven. Otherwise, I think we would have died of fear and terror.

Lucia's Vision of Hell

 Fr. Martin Von Cochem (1900): “It has now been made clear that the damned will one day be cast, body and soul, into the huge and awful furnace of hell, into the immense lake of fire, where they will be surrounded by flames. There will be fire below them, fire above them, fire round about them. Every breath will be the scorching breath of a furnace. These infernal flames will penetrate every portion of the body, so that there will be no part or member, within or without, that is not steeped in fire.” (The Four Last Things., p. 120)