From the Introduction:
Humanity lives in the mountain peaks of an unforgiving world of storms. Lightning streaks the turbulent sky and residents long ago became used to the periodic claps of thunder that follow them. Men built their cities in the peaks to escape the acidic fog that blankets the world. A man can survive in the mists, but not comfortably and not for extended periods of time. Skin burns and sloughs away, equipment doesn't last and the water... well, best to avoid drinking it.
Humans can't easily survive in the depths, but that doesn't mean that the world's natural inhabitants haven't adapted. There are strange, pale forests blanketing the mountains. They team with unusual and evasive life. Few men have gone deeper than the forests, those that have come back changed and speak of acidic lakes, sulphuric geysers and whispers.
Cities on the Peaks
Built above the acidic rain clouds and fog that creates the depths are massive cities where the majority of humanity live. The rich rarely venture out of these cities, instead relying on the backbreaking and dangerous labour of the poor, which routinely leave the cities to gather, explore and mine.
The Pale Forest
The forest lies beneath the thick layer of clouds and blankets entire mountains. It can be a dangerous place, full of unusual creatures and deadly hazards. Despite the obvious dangers of acid injuries or attack by natives of the forest, expeditions are still sent into The Pale Forest to gather, explore, find lost miners and perform other tasks important to the survival of those in the cities.