New buildings in the 21st century must address the challenges of sustainability to remain viable and prosperous. As such, they must be versatile, functional, and meaningful. Rather than serving one specific utility, many of these structures could have mixed uses: they could operate as both commercial centers and space for residences and small studios. Your local cafe and retail outlet could exist right below your apartment. Likewise, there could be a hydroponic farm operation in the same space as the grocery store that sells the produce. More importantly, these structures must deal with the key issues of water and energy conservation, and waste processing. They must be able to produce their own energy, reuse their own water, and recycle their own waste. They might act as small micro-communities that are decentralized, yet still intimately connected to the city as a whole. This is one of many different ways to reimagine structures for the 21st century.