Perelandra — C.S. Lewis

In Perelandra, Elwin Ransom, the hero of Out of the Silent Planet travels to Venus at the request of Oyarsa, the angelic ruler of Malacandra (Mars). After arriving, he meets the queen of Venus, an Eve-like being named Tinidril who rules over the unspoiled paradise of floating patches of vegetation on a sweetwater sea. When Professor Weston appears on Perelandra, Ransom must overcome his old nemesis' deception to save Tinidril and her planet from corruption. The second book of Lewis' Space Trilogy, it was first published in 1943.