Early on the works of the Slith were almost completely lost during a a great purge by a religiously fanatical warlord. Ages passed and the stories of the ancient Masters drifted into that of fairy tale.
Recently on a large, barely populated island there was an amazing discovery. Hanging in the air above a secluded valley was what seemed to be a floating city. In the valley below were numerous Slith ruins, many of them still intact. The locals have avoided the place out of fear and superstition but some brave few are now choosing to try and unearth the lost secrets of the old Masters.
Due to a lack of access to my notebooks I thought that I'd flesh out the post apocalypse thing from earlier. While I'll be focusing on systems generic descriptions for this I have a few "larger picture" ideas in mind.
The original inspiration for this comes from a setting I was working on to use with the Radiance RPG. The PCs would be coming from the main civilized continent that somewhat resembled Europe in the 1500's (or perhaps later of I wanted to add some steam capability so that Slith tech wouldn't be quite as alien). The main external conflict in this version of the campaign would come from the warring factions back home and their interference in the PCs exploration. Does their home countries demand new weaponry? Are their rival explorers looking for secrets? Is there an external danger that could unite everyone? Or perhaps secrets that need to be destroyed for the good of the world.
Another option would be to dial the tech knob back and run it as straight up fantasy D&D. The edition would likely determine the overall feel. First edition would just be good old fashioned "Expedition to the Barrier Peaks" type of pulp. Third edition would probably be best doing something similar only less pulpy. Fourth edition could use a good antagonist who is also trying to get their hands on the secrets of the Slith, perhaps with an overall goal of trying to prevent the Slith from returning.
Finally this is where I'd use the Slith Script that I had developed for various alien instructions on ancient machinery.