I've been thinking about the Steampunk RP and how to revive it. So here is a similar idea, but in my opinion, with a more interesting setting.
It is the small mechanical planet of Utopia. Built by humanity a thousand years ago, it was meant to be the crowning achievement of mankind. A huge megastructure, it would automatically carry out experiments within its interior, and pull on geothermal energy to keep its city-size gears turning. Built in such a way that it could function in the worst of conditions, it hardly used any electricity at all, due to silicon erosion, and the need for it to exist for a very long time. Upon its surface, a utopia was grafted upon it. Apart from the occasional mile-wide steam vent, it was very much like Earth itself. It was kept free of pollution and huge structures, for its intention was to remain a garden world, with most of its citizens living in the iron interior below the surface. And as the worlds of mankind went through an environmental and political strife, Utopia remained a shining beacon of hope.
Unfortunately, it was not so.
Mankind entered a nuclear war, using weapons of ferocious proportions. The only place unscathed was Utopia. And as mankind went through an almost eternal dark age, Utopia's location was soon forgotten.
This was fine for a while, and the citizens of Utopia laughed at the rest of humanity. But they didn't laugh for long. Eventually, even the most fail-safe systems break down, and that is what happened to Utopia. Experiments, once contained, destroyed humans under the surface, and the perfect environment was ravished. The citizens of Utopia had no choice but to go to the surface to escape the chaos.
And as the rest of mankind managed to rebuild their glory, Utopia, now bitterly christened Distopia, went through its own dark age.
They lived in fear for the erratic behavior of the planet, for the barbarious bandits who mixed technology with ignorance, the very experiments that their ancestors created, and the ones that the planet was inevitably creating out on its own.
Good setting, huh? Its in a mix between steampunk and biopunk. It is steampunk in the fact that right now people are using steam technology they brought up with them to the surface, and because the planet itself is a huge clockwork machine, and it is biopunk because the experiments under the surface were mostly biological, and very dangerous. Think flesh-eating monsters, huge hives of human-sized ants, and maybe even the occasional mutant, all hell-bent on destroying what's left of Distopia, and the only thing in their way is your character with their trusty steam gun and dirigible.
So, what do you think?