I read this one in the very early 1980s, but I believe the story is much older – 50’s or 60’s. It’s very “pulp novel” in its themes and style – lots of action and adventure, little in the way of complex relationships or hard science. To use a film analogy, it’s more “popcorn movie” than art house cinema. I believe this was the first in a series of novels, but I’m not entirely sure about that point. Here’s what I can remember:
● The protagonist - an old man - discovers a horn inside a house. I’m not sure how he came by the horn, or if he lived in the house or was thinking about buying it. When he plays the horn a certain way, he accidentally opens a portal to another universe. The man, whose life is pretty miserable (nagging wife, health issues, and I think perhaps even some legal troubles) soon enters the portal.
● Once there, he discovers a tropical beach paradise. Everyone is healthy, young, and beautiful, natural food is superabundant, and the world has a “fountain of youth” effect on the old man. He begins to grow younger, gradually regaining his hair, his teeth, and so on. In a few days, he is restored to his physical peak.
● Eventually, the man learns that he is not who he thought he was. He learns he is part of a family or race of people that create pocket universes as their own personal playthings and rule them as god-like beings (albeit mortal ones). The laws of science and physics in these worlds function at the whim of the creator. Thus, in the tropical world, people do not age or get sick, being effectively immortal short of accident or violence. The man further learns he is not only one of these creators, but this world was his own creation.
● I can’t remember how the man came to Earth originally, but I think it was some sort of accident or mishap. Perhaps a form of banishment by other creators. The people who create these universes are depicted as often cruel and vain, a bit like Greek gods. The protagonist was himself very much like that, but his time on Earth as the person he thought he was has changed his nature to one more aligned with compassion and benevolence.
● The only other point that I can remember is, that there is a massive, infinitely tall mountain/spire in the center of the world. The man and I believe some companions climb this spire/mountain for several days in order to reach his fortress or kingdom above the tropical paradise. It may even be another world (not sure about that).
Any insight would be welcome!