Not much appears to actually be known about Gehenna, or Valley of the Son of Hinnom. The Old Testament identifies it as a place of idol worship and is likely synonymous with Topheth. There is some thought that it served as a garbage dump in the time of Jesus but that is not known for sure. The assumption that it had become a garbage dump does have some appeal based on its history as a place of defilement and what Jesus has to say about it.
A burning garbage dump
Jesus describes Gehenna as a place where the wicked are cast (Matt 23:33), a place where body and soul are destroyed (Matt 10:28), a place where the fire never goes out and the worm does not die (Mark 9:42-48). How like the Misterbianco dump: a place where refuse is tossed; a place that destroys whatever is cast into it; a place where the fires burn continuously; and a place where maggots and other decomposers are continuously at work.
Michelangelo's Last Judgement
In fact, apart from a couple of passages in Revelation, a writing filled with symbolism, I can find nothing in the New Testament to support the traditional view of hell being a place of eternal conscious torment for unbelievers. Rather it appears to be a place where unbelievers are completely destroyed, or annihilated. I realize this is contrary to the more traditional view, and I am open to correction here, but I just don't see eternal torture in the New Testament.
I would love to discuss this with anyone who would care to at Rational Christianity.