They're a modern retelling of sorts of Dante Alighieri's Inferno. In it, a science fiction writer dies and finds himself at the Vestibule of Hell. Throughout his journey he refuses to believe that he is in an actual hell, as he was an atheist, and tries to come up with scientific/logical reasons for the things he is seeing.
They're quite a wonderful couple of books. I've read them a few times myself. I'd say if you're a fan of Inferno you should definitely check those out. Also, check them out if you've tried to read the poem but it just went over your head almost entirely (like it did me at first). These are really two of my favorite books. I often see them just sitting there and want to read them all over again. Plus, they're both fairly short. Inferno clocks in at 232 pages. I don't think Escape From Hell is much longer. So each book can be read, easily, in a weekend.