An underwater city made of coral, rock, and shipwreck debris. Vibrant structures shaped like spirals and arches rise from the ocean floor, with bioluminescent lights illuminating the scene. Mermaids with flowing hair in seaweed green, lilac, and pastel orange swim through the city, their tails reflecting the same colors. The city is nestled in a massive underwater cove with a hidden air pocket above, where the mermaids gather to give birth and shift into human form. The image is Dark Fantasy in style. Illustration. High detail. Hyper realistic. Cinematic lighting.