Underwater fantasy worlds offer some of the most immersive and visually striking settings in the genre, where entire civilisations exist beneath the surface, shaped by pressure, silence, and the unknown. From the legendary city of Atlantis to the transformative journey in The Little Mermaid, these stories explore the tension between two worlds — land and sea — and the cost of crossing between them. In this collection, writers are invited to imagine sunken kingdoms, hidden societies, and the powerful forces that govern life beneath the waves. This set of 70 Underwater Fantasy Writing Prompts provides a complete creative toolkit, including plot hooks, title ideas, opening and closing lines, character concepts, and atmospheric setting prompts. Exploring themes of transformation, isolation, and survival, these prompts are designed to help writers build immersive worlds and develop stories shaped by the beauty and danger of the ocean.