Design a futuristic megaproject floating city bustling with people, inspired by an abstract, biophilic representation of a gigantic ribbed sea shell, featuring pointed, intricate details. Engineered to float gracefully on the surface of the ocean, the structure should be sleek and aerodynamic, harmonizing with its surroundings despite its intertwined, complex shapes, while offering breathtaking views of the vast, open water, complemented by surrounding water fountains illuminated with pink and powder blue lighting. Below the floating building, reveal a mesmerizing underwater city of Atlantis, alive with intersecting neon runic lines, curves and symbols, bustling streets, and advanced technology. Hints of underwater road networks should be subtly visible from above, adding to the futuristic and interconnected feel. On the surface, luxury yachts gracefully depart and arrive, their elegant lines reflected in the shimmering waters. The overall design should seamlessly blend nature, technology, and luxury, capturing both the tranquility of the sea and the dynamic energy of a thriving maritime hub.