Rainbow Mars by Larry Niven
Hmmmmmm, how do I classify this fantasy/science fiction novella and book? It involves time travel from a post-apocolyptic future to a fantasy past and space travel to Mars. Throw in a little H.G. Wells, Arthur C. Clarke, C.S. Lewis, Edgar Rice Burroughs, Robert Heinlein, and a few other classic science fiction authors, season with a Little “Jack and the Beanstalk” and other fairy tales, and Larry Niven’s wonderful imagination, and Rainbow Mars is born. It starts with the novella, Rainbow Mars, then is followed by the short stories that preceded it, shaping the world it uses as its base.
Hanville Svetz travels to the past and to Mars. He discovers a tree that reaches into outer space. His mission is to bring that tree back to future Earth. While so doing, he and his team discover some strange life. They meet other intelligent species. They start fairy tales. They destroy the Earth as they have lived in it. How do they fix everything?
Have fun with this. I enjoyed it and caught on to some of the hidden jokes. Others I missed until they were pointed out to me. Others I didn’t realize were jokes until I read Niven’s postscripts. Then I read the earlier short stories that go with it. They show the humor of being a haphazard, government guided time traveler.