The world is facing a range of critical challenges linked to population growth, including increasing demands for energy, water, and food, rising CO2 emissions, and the depletion of natural resources. Covering 70% of the Earth’s surface, the oceans present significant potential for solutions to these global challenges. The “Green Float” project, developed by Shimizu Corporation in Japan, introduces an innovative concept for sustainable, floating urban environments. This project aims to create self-sufficient, zero-carbon, and zero-emission cities on artificial islands. The envisioned structure comprises a 1000-m-tall mega-tower and a 2000-m-diameter floating base, strategically located near the Equator to reduce risks from waves and strong winds while optimizing renewable energy potential. Construction planning and technical development have been carried out to realize the floating structure offshore. Extensive research, including hydraulic model experiments and numerical simulations, has demonstrated the feasibility and safety of a scaled-down version, Green Float II, designed for shallow coastal waters. These studies confirm the structure’s resilience against extreme weather conditions and tsunamis, supporting the project’s vision of sustainable and innovative urban development.