Although faith tells us nothing definite regarding the location of Purgatory, the most common opinion, that which most accords with the language of Scripture, and which is the most generally received among theologians, places it in the bowels of the earth, not far from the Hell of the reprobates. Theologians are almost unanimous, says St. Robert Bellarmine, in teaching that Purgatory, at least the ordinary place of expiation, is situated in the interior of the earth, that the souls in Purgatory and the reprobate are in the same subterranean space in the deep abyss which the Scripture calls Hell. (Catech. Rom., chap. 6, § 1)
When we say in the Apostle’s Creed that after His death Jesus Christ descended into Hell, the name Hell, says the Catechism of the Council of Trent, signifies those hidden places where the souls are detained which have not yet reached eternal beatitude. But these prisons are of different kinds. One is a dark and gloomy dungeon, where the damned are continually tormented by evil spirits, and by a fire which is never extinguished. This place, which is Hell properly so called, is also named Gehenna and abyss.
There is another Hell, which contains the fire of Purgatory. There the souls of the just suffers for a certain time, that they may become entirely purified before being admitted into their heavenly fatherland, where nothing defiled can ever enter.
A third Hell was that into which the souls of the saints who died before the coming of Jesus Christ were received, and in which they enjoyed peaceful repose, exempt from pain, consoled and sustained by the hope of their redemption. They were those holy souls which awaited Jesus Christ in Abraham’s bosom, and which were delivered when Christ descended into Hell. Our Savior suddenly diffused among them a brilliant light, which filled them with infinite joy, and gave them sovereign beatitude, which is the vision of God. Then was fulfilled the promise of Jesus to the good thief: This day thou shalt be with me in Paradise.
“A very probable opinion,” says St. Thomas, “and one which, moreover, corresponds with the words of the saints in particular revelation, is that Purgatory has a double place for expiation. The first will be destined for particular cases, and it is from thence that so many apparitions occur.” (Suppl., part. 3, ques. Ult.).
The holy doctor admits, then, like so many others who share his opinions, that sometimes Divine Justice assigns a special of purification to certain souls, and even permits them to appear either to instruct the living or to procure for the departed the suffrages for which they stand in need; sometimes also for other motives worthy of the wisdom and mercy of God.
Such is the general view concerning the location of Purgatory. Since we are not writing a controversial treatise, we add neither proofs nor refutations; these can be seen in authors such as Suarez and Bellarmine. We will content ourselves by remarking that the opinion concerning a subterranean Hell has nothing to fear from modern science. A science purely natural is incompetent in questions which belong, as does this one, to the supernatural order. Moreover, we know that spirits may be in a place occupied by bodies, as though these bodies did not exist. Whatever, then, the interior of the earth may be, whether it be entirely of fire, as geologists commonly say, or whether it be in any other state, there is nothing to prevent its serving as a sojourn of spirits, even of spirits clothed with a risen body. The Apostle St. Paul teaches us that the air is filled with a multitude of evil spirits: We have to combat, says he, against the spirits of wickedness in the high places. (Eph. 6:12)
On the other hand, we know that the good angels who protect us are no less numerous in the world. Now, if angels and other spirits can inhabit our atmosphere, whilst the physical world is not in the least degree changed, why cannot the souls of the dead dwell in the bosom of the earth? (From Purgatory by Fr. F. F.X. Schouppe, SJ)