What is the main setting in the novel, Girl in Landscape?

The vast majority of the novel takes place on the Planet of the Archbuilders. In the story, humans discovered this planet relatively recently, and they have established a few small settlements. The planet was originally inhabited by an advanced species referred to as the Archbuilders. The Archbuilders managed to alter the environment to always be temperate and to furnish a consistent supply of food. Most of the Archbuilders left the planet years ago in order to explore other areas of outer space.