The Conquest Of The Rustumite Lowlands

Poul Anderson's Rustum History comprises nine stories, including "The Queen of Air and Darkness," which is set on a different planet but in the same timeline. Like many other series by Anderson, this future history could have been extended indefinitely but then he would have written less of something else.

Numbering the nine stories, 1-9, we find the conquest of the Rustumite lowlands in three stages in 4-6:

in 4, two men rescue a child, Daniel Coffin, who has wandered down into the lowlands;

in 5, two men, including the teenage Daniel Coffin, salvage equipment from an aircraft that has crashed in the lowlands;

in 6, the adult Daniel Coffin lives in a lowlands station with pastures and grainfields and must marry someone who, like him, can live comfortably in the higher air pressure of the lowlands.

Thus, Anderson presents a systematic narrative. Environmental details originating in earlier stories provide background in 6, e.g.:

the large moon, Raksh;
the small visibly moving moon, Sohrab;
Sol, seen as a star, not as the local sun.

Other planets cast glades on the lake.