Euclid's Wall, by Michael McCollum
Michael McCollum has been self-publishing for many years - since at least 1997 - in both paper and alectronic formats. His books (this is the tenth I've bought) are mostly space opera. They don't really stand out from the crowd, but are entertaining enough. This, however, is a bit of a departure from his norm, being set on a post-Apocalyptic Earth.
After an experiment into novel new energy sources went horribly wrong, Earth was wracked by terrible earthquakes and beset by huge tsunamis and civilisation fell. But as the years passsed, things calmed down, the survivors regrouped, and society is at roughly the level of the late 17th century by the time of the tale. The tale is one of exploration and a search for resources and information about the calamity that befell the "high civilisation", which turns into a desperate scramble to save the world. How convenient that European civilisation had managed to claw its way back up to a level at which it could save the world with an expedition half way around the globe, and at just the right moment!
The coincidence that allows our heroes to be heroic is ridiculous, of course, but that is the nature of books that have heroes. Heroes are never believable. Everything else is plausible (fanciful, perhaps, but at last plausible) and it's a rollicking good story that you will want to polish off quickly, and so I recommend it.
And the world he creates for this book would easily support a host of other stories, either in series or stand-alone. I hope that he writes them.