Structure with huge sound amplifiers where people from all corners of the earth give a mass concert to fill the whole planet with music.
Green roads sustained by the vehicles themselves which irrigate nutrients and moisturize the ground in their path.
Lighting system made of smart materials which illuminate the place only when somebody walks between them. This system has been designed to eliminate light pollution. During the day this system is hidden and captures daylight to work at night.
Self-governing machines which are huge generators, storing the electricity that generates the water by itself. After that, they move to the areas where those energy are needed.