Earth Made of Glass
In A Million Open Doors, John Barnes introduced the universe of the Thousand Cultures - in which, a thousand years hence, humanity's hundreds of settled worlds are finally coming back into regular contact with one another via the recently invented "springer," which affords instantaneous travel between worlds separated by light-years. But reknitting mankind's diversity is a challenging task, requiring skill, ingenuity, and the patience of professional diplomats. Which is what Giraut and Margaret have become, twelve years after the events of A Million Open Doors. Now their task is to bring into the community of the Thousand Cultures the one human world that has yet to build a springer - the terrifyingly hostile world of Briand, a planet of boiling acid oceans whose only habitable portions are Greenland-sized sub-continents that project out of the heat of the planetary surface into its temperate stratosphere.