Concrete shells are thin, curved structures made from reinforced concrete. They are designed to be lightweight yet strong, allowing them to span large distances without the need for extensive support. This makes them ideal for various applications, including roofs, bridges, and even sculptures. The construction of concrete shells often involves techniques like formwork and pre-stressing, which enhance their durability and stability. Notable examples of concrete shells include the Sydney Opera House and the Geodesic Dome, showcasing their aesthetic appeal and functional versatility in modern architecture.