Writers who truly listen know there are areas that they must avoid. It is the fools who rush in where the wise fear to tread. While I feel like I have learned a lot about heaven from C.S. Lewis, he seems to have an invisible boundary in his writings, keeping him from entering it. In The Great Divorce the visitors only come to the outlands of heaven. Heaven proper is across the plain and over the foothills. We face something similar in The Last Battle. The author ends the story on the outer reaches of heaven because he can take us no farther. Lastly we can see this in the fact that Lewis never published an opposite version of The Screwtape Letters, one from an angelic perspective. He knew himself well enough to know that it was something he did not have the ability to do.
J.R.R. Tolkien too was aware of this boundary I think. We find it in a short allegory Tolkien wrote called Leaf by Niggle (Tolkien did on the whole dislike allegories but he clearly intended this story to be read as such). Niggle goes through his life and then on to a sort of two-step purgatory (Tolkien was Catholic by the way). The story ends with Niggle leaving on a journey into the mountains. Always they have been on the verge of his horizon, but with his purging complete the time has come to move on to them. Tolkien knows his skill and his humanness enough to know he can take us no farther.
Dante is the only writer I know who dares to cross that line and perhaps has the skill to do it. In my opinion The Divine Comedy is one of the most sublime works of literature ever written. Still, Paradiso is the driest book of the Divine Comedy, containing more discourses than the others. How do you describe heaven in the manner it deserves? In the end Dante cannot bring himself to describe God Himself. We are left to see the reflection of His glory in the other inhabitants of heaven. You could say that God is heaven or at least what makes heaven heaven.
The Bible itself is a little shy about heaven. What we know of it has been pieced together from hints scattered throughout the Bible. Still there is not as much description as I would have liked. I find myself unsure of what to take as a picture of what heaven is actually like and what is heaven as God has presented it in a form that mortal, fallen human beings can grasp. Many of the eschatological frameworks I have seen that try to fit together things like the Resurrection, the thousand-year reign of Christ, the Judgment, and the New Jerusalem end up like a blanket that is too small. When you finally succeed in covering one area, another is left out in the cold. What I do know is that heaven is some place that I long to go.