With space in many urban areas at a premium, one idea that is gaining traction is to build down instead of up, creating underground cities.
While the prevailing logic in building new structures in crowded urban centers is to build ever upwards, even into space if some designers get their way, some cities are considering heading in a different direction altogether.
Straight down.
Building underground is not exactly a revolutionary concept, but the scale of some new proposals are almost unheard of. We’re not talking about a small, Hobbit-style home built partially underground. But instead, full buildings designed to both create more space in an overcrowded urban environment and combat the elements. Some designers are even developing massive structures, known in some circles as “Earthscrapers,” which will be part of a movement downwards to create underground cities hidden beneath existing ones.
In some locations, this idea of underground cities and towns is already very much a reality, although the scope is much less grand. For example, the majority of the Australian mining community of Coober Pedy already exists below the surface.
Coober Pedy is located in a remote and desolate corner of Australia, but its claim to fame is that it is home to the largest Opal Mine in the world. Nearly 3,500 residents live and work in the desert town, which has been known to see temperatures of 122º Fahrenheit during the day and 31º at night.
To protect themselves from the elements and thanks to limited resources, the locals began to create “dugouts,” or underground homes built into and under the rocky environment. The practice began as far back as 1915 with rudimentary buildings meant for survival, but over the years a bizarre community has built up – or down, as the case may be. Residents fashion their dugouts with all the trappings of any other town, including electircity, heating, carpets, and more. 
To outsiders, it may seem like a strange way to live, but soon the people of Coober Pedy may be seen as trendsetters of a sort.
Several cities around the world are considering going down as populations go up. One prime example is Singapore, which supports a population of around 5.5 million, all living in an area of just 710 square kilometers. To put that in context, the city of Los Angeles (not counting the metro area) has a population just shy of 4 million spread out over 1,213.9 square kilometers.
Singapore is also growing at a rapid pace thanks to a surging economy. That means city officials are looking for new ways to make the most out of their limited space. One plan currently being considered in Singapore is the Underground Science City (USC), a 300,000 square meter research and development facility focusing on biomedical and biochemistry projects. If approved, the structure would inhabit a space 30-80 meters below ground, with downward expansion a possibility.
Another city facing a similar, although much more severe situation, is Mexico City. Mexico’s capital is one of the largest cities in the world, with an estimated metro population of nearly 21 million people, most living in what is essentially one valley. In Mexico City proper, the population density is so severe that there are nearly 25,300 people living in each square mile. One answer to this problem is to build downward.
The architecture firm Arquitectura recently introduced plans for a 300-meter deep inverted pyramid dubbed the “Earthscraper.” The structure would house 5,000 people and feature an open, glass ceiling to let in light. The lower levels, however, would need additional lighting. It is still just a concept at the moment, but with population density increasing, it may move forward sooner rather than later.
Another country constantly battling population issues is China, which features the most “mega-cities” in the world. China is already committed to building underground, for better and worse. In Beijing, a wildly vague estimate places the current underground population at anywhere between 150,000 and 2 million residents. The styles of these underground domiciles range from luxurious to squalor, with many people forced to live underground rather than choosing to, but that may slowly change.
Building underground has its risks and rewards. It is one way to get around space constraints, and there are environmental advantages, including natural insulation and protection from the elements. The big downside, however, is the cost. Building underground structures from scratch (as opposed to building in caves, for example), mean builders will have all the costs associated with a standard structure, as well as those attached to building down. That includes removing the earth and ensuring the safety of workers.
Still, it is an intriguing idea, and one that may continue to gain popularity as the population around the world continues to rise.