The Desert is what each mortal soul must traverse after death. No-one knows what's at the end - and Death isn't saying, if he indeed knows. After all, he has never, in-fact, died. It would be immensely fascinating to find out what TP believes is over the desert, past the distant mountains.
The one tantalising clue that is left in a few of the books is that you get what you think you deserve. So Valhalla is available to Barbarian heroes, paradise awaits Klatchians and so on and so forth.
This seems to negate the possibility of a Hell or hells, although Rob Anybody Mac Feegle insists they've been to a few such places (and through various versions of limbo too [so called - hilariously - because the door in was verrae low, ye ken?]). It seems that if you think you deserve hell you'll get it. Deeply unfairly, the only people who ever think they deserve hell are those poor worried souls who have always tried to do good and have always been meek but are afraid all their lives that they haven't done well enough. However fair this is, or seems, There is no justice. There's just Me.
In other books, though (notably Eric), everybody seems to be in Hell (which also seems to be a corporeal place) after death. And in others there seem to be parallel dimensions where people in between exist: ghostly netherworlds, such as those inhabited by One-Man-Bucket.
And what of the rat-catcher Pounder in Maskerade and Mr. Clete in Soul Music , who on their death do not go to the Desert at all: The Death of Rats gleefully leads them to the revolving door marked Serially Reincarnate as Rat until further notice?
Warriors still bypass the Desert and go to Valhalla ( as seen in Soul Music, Interesting Times and The Last Hero), while the crew of the ship wantonly wrecked by Vorbis in Small Gods proceed to sail a nautical equivalent of the Desert for all eternity.
The possibility is there that this is the "default" afterlife for those who in life had no religious conviction, nor a religio-cultural inner picture of what form the Afterlife would take.
The Desert is of greyish-black sand, which fountains slowly through the air when disturbed. At the far end are distant mountains, under a starless sky. Everyone must walk it alone.
Notable visits to The Desert
- Vorbis - for all his bluster and self-confidence - was too scared to walk it alone. One hundred human years later Brutha forgave and helped him (Small Gods). And human years have no relevance. Vorbis may well have been there for eternity, trapped by his own revealed self-knowledge, and have been too frightened to face the judgment he expected.
- Anghammarad didn't want to leave the desert because in it he found perfect peace away from orders and commands. He was - finally - free, and he just wanted to stay (Going Postal).
- Tiffany Aching took the Hiver to The Desert and set it free (A Hat Full of Sky). She escaped thanks to Granny Weatherwax.
- Granny Weatherwax - and many of the witches - have been here before, to help others shuffle off their mortal coils, and have found their way back.
- Lord Hong - While his visit is not shown, it is mentioned that his desert contains a lot of angry ghosts, and that every person's desert is of varying distance.
I have to walk that lonesome valley/I have to walk it all alone These are lines from a fundamentalist Christian hymn which occur in the book (the word "valley" in the original becomes "Desert" on the Discworld, though) when Brutha has to confront the idea of walking through the Desert (both on the physical Discworld and when ushered by Death into the Afterlife). It's certainly popular: a lyrics site lists sixty different recordings, perhaps the most prominent of which was by Elvis Presley:-
In Robert Anton Wilson's Illuminatus! trilogy, the same verse of the same hymn is used when two of the principal characters are forced to question, challenge, and finally reject the Christian orthodoxy they have been brought up to believe in. Like Brutha, both Robert Putney Drake (villain) and Hagbard Celine (anti-hero) experience the absolute loneliness of being leaders, responsible not just for themselves but for the fortunes of others. Drake, like Vorbis, ends up in a Hell of his own making, while Celine finds a sort of inner peace based on his philosophy of "Think for yourself, schmuck!" - not a million miles away from the philosophy into which Brutha steers Omnianism.