by Jack L. Chalker – 1977

The Well World is a planet-sized computer that acts both as the controller of and the gateway to 1560 worlds created by an ancient and extinct alien race.

Answering a distress call, starship captain Nathan Brazil and his passengers are suddenly transported to the Well World by a hidden gate.

There, Nathan Brazil must stop mysterious forces from taking control of the Well World, and through the Well World, the universe. But to do so, he must deal with bizarre transformations, which have changed people into centaurs, mermaids, and giant insects. In this strange land, inhabited by these strange, transformed creatures, he doesn’t know who are his friends, and who are his enemies. And what of his own memories, which seem to have been deeply suppressed?