The Divine Comedy is a piece of literature written by written by Itallian poet, Dante Alighieri.
I'm not entirely sure of the whole story myself, but it involves the telling of Dante's journey through the three realms of the dead, the first of which being Inferno, or Hell, including all of it's nine circles, the second is Purgatorio (Purgatory) and Paradiso, which is basically Heaven.
In Hell, Dante comes across Virgil (Vergil, see the link? :lol
who is sent to be Dante's guide through the Nine Circles of Hell.
That's basically all I know of The Divine Comedy, but I could suggest a search on Wikipedia for more information on the subject.