According to some narrations. Hell is beneath the earth. As we have explained in other places in its annual orbit the globe of the earth traces a circle around an area that in the future will be the place of the Great Gathering and Last Judgement. It means Hell is beneath the area of its orbit. It is invisible and unperceptible because it consists of veiled and lightless fire. In the vast distance traveled by the earth are many creatures that are invisible because they are without light. Like the moon loses its existence when its light withdraws so we are unable to see numerous lightless globes and creatures which are before of our eyes.
There are two Hells the Lesser and the Greater. In the future the Lesser will be transformed into the Greater and is like its seed; in the future it will become one of its habitations. The Lesser Hell is under the earth that is at the earth's center. It is the inside and center of the globe. It is known in geology that in digging downwards the heat for the most part increases one degree every thirty-three meters. That means that since half the diameter of the earth is around six thousand kilometers the fire at the center is at a temperature of around two hundred thousand degrees that is two hundred times hotter than fire at the circumference; this is in agreement with what is related by Narrations. This Lesser Hell performs many of the functions of the Greater Hell in this world and Intermediate Realm and this is indicated in Narrations. Just as in the world of the hereafter the earth will pour its inhabitants into the arena of the resurrection within its annual orbit so too at the Divine command will it hand over the Lesser Hell within it to the Greater Hell.
Some of Learned people said that "Hell will be created later." but this is mistaken and foolish and arises from Hell not having completely opened up at the present time and developed into a form entirely appropriate to its inhabitants. In order to see with our worldly eyes the dwelling places of the world of the hereafter within the veil of the Unseen and to demonstrate them either the universe has to be shrunk to the size of two provinces or our eyes have to be enlarged to the size of stars so that we can see and specify their places. God knows best the dwelling-places of the hereafter are not visible to our worldly eyes but as indicated by certain narrations the Hell of the hereafter is connected with our world. In a Narration it is said of the intense heat of summer. "It gives an inkling of Hell." That is to say that Greater Hell is not visible to the tiny and dim eyes of the minds of this world. However we may look with the light of the Divine Name of the All Wise as follows:
The Greater Hell beneath the earth's annual orbit has as though made the Lesser Hell at the earth's center its deputy and made it perform some of its functions. The possessions of the All-Powerful One of Glory are truly extensive; wherever Divine wisdom pointed out. He situated the Greater Hell there. Yes an All-Powerful One of Glory an All-Wise One of Perfection Who is owner of the command of 'Be!' and it is has tied the moon to the earth before our eyes in perfect wisdom and order and with vast power and perfect order tied the earth to the sun and has made the sun travel together with its planets with a speed close to that of the annual rotation of the earth and with the majesty of His dominicality according to one possibility made it travel towards the sun of suns and like a fleet decked out with electric lights has made the stars luminous witnesses to the sovereignty of His dominicality. It is not far from the perfect wisdom tremendous power and sovereignty of dominicality of one thus the All-Glorious to make the Greater Hell like the boiler of an electric light factory and with it set fire to the stars of the heavens which look to the hereafter and give them heat and power. That is give light to the stars from Paradise the world of light and send them fire and heat from Hell and at the same time make part of that Hell a habitation and place of imprisonment for those who are to be tormented. Furthermore. He is the All Wise Creator Who conceals a tree as large as a mountain in a seed the size of a fingernail. It is surely not far then from the power and wisdom of such an All-Glorious One to conceal the Greater Hell in the seed of the Lesser Hell in the heart of the earth.
In Short: Paradise and Hell are the two fruits of a branch of the tree of creation which stretches out towards eternity. The fruits' place is at the branch's tip. And they are the two results of the chain of the universe; and the places of the results are the two sides of the chain. The base and heavy are on its lower side the luminous and elevated on its upper side. They are also the two stores of this flood of events and the immaterial produce of the earth. And the place of a store is according to the variety of the produce the bad beneath the good above. They are also the two pools of the flood of beings which flows in waves towards eternity. As for the pool's place it is where the flood stops and gathers. That is the obscene and filthy below the good and the pure above. They are also the two places of manifestation the one of beneficence and mercy the other of wrath and tremendousness. Places of manifestation may be anywhere; the All-Merciful One of Beauty the All-Compelling One of Glory establishes His places of manifestation where He wishes.
As for the existence of Paradise and Hell they have been proved most decisively in other Q & A sections. Here we only say this: the existence of the fruit is as definite and certain as that of the branch; the result as the chain; the store as the produce; the pool as the river; and the places of manifestation as definite and certain as the existence of mercy and wrath.
"Say: the knowledge is with God alone.... None knows the Unseen save God."