The post Bl. John Paul the Great conception of purgatory was that it is a 'state' and not a place. So whatever, private revelation I allude to in the following sentences are not indiciative of universal Catholic doctrine (if you find any please report it to the dept. of redundancy dept)
It would seem that Purgatory is For the soul's purification in the fires of God's love. The souls in Purgatory are referred to as the Church Suffering and the suffering experienced in Purgatory will take place for a predetermined length (until the last penny is paid). The only way out of Purgatory is up to heaven. The souls in Purgatory do not haunt the living. But the intercessory prayers of the living may reduce the time spent of a soul in Purgatory. Such Indulgences may be applied either to the person seeking the indulgence, or purposes of lessening their own time in Purgatory or for a soul in Purgatory. A partial indulgence is what one gets when making the sign of the cross or praying a certain prayer or doing a spiritual or corporal work of mercy.
Prayers for souls in purgatory
A plenary indulgence is complete removal of the time spent in purgatory and it can be applied to a soul in purgatory. But it requires a confession with perfect contrition, which is no easy task. Nevertheless an imperfectly attained plenary indulgence is in effect a pretty good partial indulgence.
some more info about saints and others who saw souls in purgatroy
You might also want to check out St Catherine's Treatise on Purgatory I believe it was her who saw souls leaving Purgatory whenever "Lord Have Mercy" was said at Mass.
Someone else'll probably mention it if I don't, but C.S. Lewis' Great Divorce certainly seemed like a souls progression through Purgatory. Even though he denied it was supposed to be that exactly.
Likewise, The Man Who Was Thursday by G.K. Chesterton is pretty Purgatorial. A lot of folks who suffer quite a bit in this world might also be likely to tell you that they're offering up their suffering so as to spend their Purgatory on Earth.
I'd love to read more old Catholic fiction on the subject, but so I hope someone else answers.
One thing you could do to further your studies is to search the Golden Legend for hints at Purgatory.
One last word, since a soul in Purgatory is not a ghost don't try to talk to them, you're more than likely talking to a demon.