Jason Lee's character in Dogma brings this up. He said that initially Hell was just the absence of God (which in itself is said to be painful), but once humans got there they were so unable to forgive themselves and live without the divine presence that they turned it into a place of unimaginable pain and suffering.

I don't think that's supported by the Bible and I'm not sure if that's a position that was even put forth by later Christian thinkers, but it's all mythology to me anyway and I find the different interpretations interesting.