The Atlantropa Articles by Cody Franklin, better known as the guy who runs AlternateHistoryHub.
Got super hyped years ago when the trailer dropped, bought the book when it came out, read through it, it fucking sucked. The writing was just plain dry, the story was boring and failed to utilize the setting in any meaningful way, the setting itself was just plain nonsensical, the handling of the issues surrounding, you know, Nazi-dominated Europe after a literal thousand years are pretty heavy-handed (I will give it credit for not being significantly apologetic or fawning in any way, but that's not exactly a high bar), and the characters are utterly flat. The entire thing feels like something you would write in high school to try and be as edgy and gruesome as possible with Nazi Europe as just a vehicle to be edgy and gruesome.
So, to spoil it, the story takes place in Nazi-ruled Europe several thousand years after Hitler's rise to power. The idea is that Hitler, rather than pursuing his aims through war, unites Europe diplomatically somehow under Herman Sörgel's vision of Atlantropa, a project to drain the Mediterranean and make way for a new continent to be settled by Europe. However, the vision soon turns out to be an utter nightmare, as what was supposed to become a fertile continent was predictably covered in salt, leaving a salt flat the size of a sea across which the Sahara expands into Europe.
In the unspecified far future, our main characters are a pair of brothers working for the German government in order to resupply an outpost on the edge of North Africa after it's been raided by "Jews" (in quotation marks for reasons which I will soon explain). The main character/narrator is an up-and-coming member of the Nazi party who has ambitions back in Berlin, while his brother owns and runs a sailing ship on wheels which they use for the resupply mission across the Mediterranean salt plain.
A short while after departure, their ship on wheels is raided by another group of "Jews" on another ship, which they manage to destroy and kill the entire crew of except for a lone survivor who they take prisoner. For the remainder of the journey the main character attempts to talk to and understand the "Jewish" prisoner, who speaks very little German, while his older brother running the ship and his crew continue to torture and interrogate him in spite of the main character's hesitation.
As it turns out, the "Jews" who have been raiding German outposts aren't Jews at all, they're the descendants of Southern Europeans and Arabs whose homelands were also ruined by the Atlantropa project. However, before anything further can be explained the older brother and his crew kill the prisoner in horrifically described detail as the main character begs them to stop.
Finally, several miles out from the outpost, their ship breaks down due to damage from the earlier raid, and the two brothers have to set out in a smaller lifeboat-type vehicle for the final stretch in order to get help. Eventually this too breaks down just before arrival and they end up having to walk the home stretch in the unforgiving salt plain heat. The younger brother, just by happenstance right before they would have died stumbles across the hatch to a ship buried in the sand they can use for shelter.
The brothers go inside, and just by more happenstance this happens to be an ancient shipwreck from the initial days of Nazi Europe. The younger brother, to his disbelief, finds photos and documents detailing the founding of the regime known in his time only through legend. He's utterly shocked to see that the Jews of old Europe looked nothing like the ones he's seen in his time, as well as by photos of Hitler showing him not to have blond hair and blue eyes as he had always seen, but of course the actual face of Hitler we all know. Finally, he finds a detailed report of the Madagascar Plan, in which the Jews of old Europe were deported to Madagascar to die, and is utterly appalled, this being the straw that finally breaks his faith in the regime.
However, in the time he's been finding out the history of Europe that's been lost for a thousand years, his brother has managed to hail a passing ship on its way to the outpost for help, and when the younger brother voices his loss of faith in the Nazi regime he promptly joins the crew of the ship in stringing up his own brother to die in excruciating fashion without hesitation, the book ending with a first person description of being dragged behind the ship along the scorching salt flats by a rope until he dies.
Yeah, the whole thing is, as you could probably tell from this description, an utter fucking mess.