In Madrid, Spain they are currently building a huge structure called an “Air Tree” or “Eco Boulevard de Vallecas”. The Tree was created by Urban Ecosystem to be a social center, and to improve the surrounding environment. The structure is also completely self-sufficient, generating all its own power with solar cells. Any surplus energy is sold to the electrical grid. It also produces oxygen using its arrays of plants and trees, hence the “tree” appellation. The designers say:

…Simple air conditioning systems installed in the air tree are evapotranspirators. This is a natural way to air condition a space, not a part of commercial strategy. Rather, it creates naturally conditioned spaces between 8-10°C cooler than the surrounding streets where the residents can take active part in the public domain.

The structure itself was made of mostly recycled materials.

Via: Urban Ecosystem Blog via Green Line Blog