Hand of the Automaton
The basic idea I had was that the greatest wizard who ever lived pulled a tower from the bowels of the earth. He didn’t build it per se, it just erupted out of the ground fully-formed, and he lived there and did experiments and research for years (decades? centuries?).
He developed all new magic, creatures, and filled his library with knowledge and lore, but he didn’t really interact with the outside world, he didn’t suffer visitors or apprentices, and he didn’t share any of his knowledge or power.
Meanwhile, the main kingdom or empire or whatever carried on, they had magic but mostly weak stuff, no really advanced knowledge, no great practical applications, and other powerful wizards were just as reclusive and just as unhelpful.
So they went more the technology route, developed steam power and combined with minor magic starting creating clockwork and steam creations. Eventually, they got greedy for the wizard’s power, built an army of automatons and attacked his tower, setting off a massive war that lasted decades and permanently impacted the entire world.
The wizard fought back with chimerical creations, mutants and freaks created by magic and alchemy. Whole areas of the world were contaminated, most of the empire’s infrastructure, including their railways and roads were wiped out. An entire sea was drained and evaporated, and the whole world essentially took a few steps back in terms of development and quality of life.
Eventually, the wizard was defeated, and the empire’s automaton armies took the tower, only to have the whole thing sink back into the ground inaccessible, denying the victors their spoils.
The game would start thereabouts, the war is over but the world is an unholy mess. Although the wizard and his tower are gone, mutants still have free rein over much of the world, they aren’t disappearing as everyone had hoped, and the remnants of the automaton armies are still around too, some having gone completely rogue whether due to the magic influence all over the place or who knows.
The empire’s propaganda machine would make it so that everyone thought this mad wizard had started the war and led to all this, although he was never an aggressor, just an aloof man sitting in his tower, apathetic towards the entire world.
The player would perhaps be on a mission from the government to figure out why the mutants are still multiplying? To try to find the source and help restabilize the world? Help rebuild the rail (to be used like waypoints) as well? Stuff like that.