Sister Lucy of Fatima saw Hell: that's how it is made. From his writings

In Fatima the Blessed Virgin Mary told the three little visionaries that many souls go to hell because they have no one to pray or make sacrifices for them. In her memoirs Sister Lucy describes the vision of hell that Our Lady showed to the three children in Fatima:

“She once again opened her hands, as she had done the previous two months. The rays [of light] appeared to penetrate the earth and we saw like a vast sea of ​​fire and we saw the demons and souls [of the damned] immersed in it. Then there were like transparent burning embers, all blackened and burned, with human form. They floated in this great conflagration, now thrown into the air by the flames and then sucked up again, along with large clouds of smoke. Sometimes they fell on each side like sparks on huge fires, without weight or balance, between cries and moans of pain and despair, which terrified us and made us tremble with fear (it must have been this vision that made me cry, as people who say me heard). The demons stood out [from the souls of the damned] for their terrifying and repellent appearance similar to that of hideous and unknown animals, black and transparent like burning embers. This vision lasted only a moment, thanks to our good Heavenly Mother, who in her first appearance had promised to take us to Heaven. Without this promise, I believe we would have died of terror and fright. "