To those who said that they did not believe in hell, Padre Pio always responded “Don’t worry my friend, you will when you get there”!
Our Lady at Fatima not only showed the children a vision of hell but showed them that many souls were already there.
“She opened Her hands once more, as She had done the two previous months. The rays [of light] appeared to penetrate the earth, and we saw, as it were, a vast sea of fire. Plunged in this fire, we saw the demons and the souls [of the damned]. The latter were like transparent burning embers, all blackened or burnished bronze, having human forms. They were floating about in that conflagration, now raised into the air by the flames which issued from within themselves, together with great clouds of smoke. Now they fell back on every side like sparks in huge fires, without weight or equilibrium, amid shrieks and groans of pain and despair, which horrified us and made us tremble with fright (it must have been this sight which caused me to cry out, as people say they heard me). The demons were distinguished [from the souls of the damned] by their terrifying and repellent likeness to frightful and unknown animals, black and transparent like burning coals. That vision only lasted for a moment, thanks to our good Heavenly Mother, Who at the first apparition had promised to take us to Heaven. Without that, I think that we would have died of terror and fear.” Our Lady also indicated (I recall reading) that many of the soldiers who had died in the First World War were in hell, mainly for sins of impurity.
I would recommend that you read some of the accounts of near death/death experiences by e.g. Howard Storm and Mark McCormack.