The Gaea Trilogy is a series of books written by American author John Varley that take place in a made-up world called Gaea. In this world, Gaea (who is essentially the planet itself) is a sentient being with the power to control time and space.
There are three books in the series: Titan, Wizard, and Demon. In the first book, a group of humans travels to Gaea and discovers that the surface of the world is actually a massive artificial structure built by an ancient civilization. They also discover that Gaea has created several creatures with extraordinary powers, including a giant named Gaby and a sphinx named Tabor.
In the second book, the humans return to Gaea and discover that the world is threatened by an entity called the "Wizard," who wants to destroy Gaea and remake the universe in his own image. The humans team up with Gaby, Tabor, and other creatures to stop the Wizard and save Gaea.
In the third book, the humans and creatures of Gaea face off against a new threat: the "Demon," a being that looks like a giant insect and wants to destroy all life on Gaea. The humans and creatures band together once again to stop the Demon and save the world.
Throughout the series, readers learn about Gaea's history and the various creatures that inhabit the world. The books also explore themes like the nature of consciousness, the relationship between humans and technology, and the consequences of playing god.