It is interesting to note that death and hell (the grave) are cast into the lake of fire -and that the last enemy to be destroyed is death.
Rev 20:14 And death and hell were cast into the lake of fire.
1Co 15:22 For as in Adam all die, even so in Christ shall all be made alive.
1Co 15:23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming.
1Co 15:24 Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.
1Co 15:25 For he must reign, till he hath put all enemies under his feet.
1Co 15:26 The last enemy that shall be destroyed is death.
Christ described the general situation of Gehenna.....
Luk 16:22 And it came to pass, that the beggar died, and was carried by the angels into Abraham's bosom: the rich man also died, and was buried;
Luk 16:23 And in hell he lift up his eyes, being in torments, and seeth Abraham afar off, and Lazarus in his bosom.
Luk 16:24 And he cried and said, Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame.
Luk 16:25 But Abraham said, Son, remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented.
Luk 16:26 And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence.
So -those cast there are not comfortable/unpleasant -though whether there are literal flames/the intensity thereof, etc, I don't know -but the real question is that of duration. Is it truly with no possibility of end -or is it dependent upon something? Is the torment of the individual without end -or is the torment itself eternal -and the individual can eventually leave it? Given the imperfection of human language and the many verses on the subject, it isn't simple to determine, but the following do suggest that while the ultimatum is eternal, the individual experience of it need not be.....
1Co 3:15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
Rev 21:8 But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.
We have all lied -even the apostles probably lied -so repentance is an issue to be considered.
Can one repent after having been cast into the lake of fire? If some in the lake of fire would go to the others, and those not there WOULD go to those in the lake of fire -out of concern, i would imagine, it does not seem like a desirable end state to me. If I'm having a great time and others are being tormented, I don't think I could feel comfortable with that eternally -and it doesn't seem to be the case from what I have read. Is it a "stay here and think about that you have done" sort of scenario?
Perhaps God is able to bring all to repentance. It is part of the mystery of God which we will eventually understand.
Rev 10:7 But in the days of the voice of the seventh angel, when he shall begin to sound, the mystery of God should be finished, as he hath declared to his servants the prophets.