The Ship of Ishtar

The archaeologist hero, Kenton, receives a mysterious ancient Babylonian artifact, which he discovers contains an incredibly detailed model of a ship. A dizzy spell casts Kenton onto the deck of the ship, which becomes a full-sized vessel sailing an eternal sea. At one end is Sharane the assistant priestess of Ishtar and her female minions, and at the other is Klaneth the assistant priest of Nergal and his male minions, representatives of two opposed deities. None of them can cross an invisible barrier at the midline of the ship, but Kenton can. His arrival destabilizes a situation that had been frozen for 6,000 years, and fantastic adventures ensue.