Jack Chalker, through this book, and the other books, tells one of the great classics in modern soft science fiction. The beginning of a five book series, Midnight tells of a man named Nathan Brazil, and how he and his strange life fit into the center of the universe and its history.
Nathan is a typically tough-as-nails starship captain who is carried through events set off by his own interference with a criminal syndicate, but it's where he goes that defines the entire series: The Well World.
The Well World is the generator of all modern reality. Billions of years in the past, a race of beings developed the ultimate in technology, computers that could read their minds, and then with matter/energy transforming systems would translate those thoughts, whatever they were, into reality. After a long time, they did everything, and became bored. They wondered if that could really be all there was to life, but could envision no more than they had, and decided that somehow they had reached an evolutionary dead end because to them it was obvious that there _had_ to be more to life. Any other decision would have meant that their lives had been meaningless. They took their computer-reality technology and built a computer the size of a planet, one so large that it could generate an entire universe. Upon its surface were hexagonal zones of a few thousand square kilometers [I can't remember the exact size], each one an enviromental enclousure where the ancient race designed and tested for viability every possible intelligent race they could think of. The designs of those that proved suitable were stored away, and the enclosure would be used again and again. Eventually they used the planet to create an entirely new universe, overlaying the original one (which had far fewer worlds and stars). The early evolution of the universe was forced through at incredible speed until most of the intelligent species emerged, and then, well, it's not exactly clear. The race that did all of it vanished, and althoug! h a variety of ideas about what happened to them were put forward in the book, none of them were convincing.
Meanwhile, in current time on The Well World, the last set of races to be tested out in the enclosures were left to their own devices. They formed odd societies and inter-society relations, given that each enclosure was often radically different from its neighbors.
Onto The Well World comes Nathan Brazil, and the passengers of his tramp freighter. Strange things begin to happen on The Well (short for The Well World). They are all told that they will be put through another gate, this one teleporting them to one of the enclosures, where they will be transformed into one of the native intelligent species.
And with that simple act, Chaos breaks out across The Well.
That sounded like the whole story, didn't it? Trust me, that's just the backfill, and spoils very little that isn't told right at the beginning of the book. And _then_ there are the next four books.