While most cities strive for a sustainable level of urban density, there are limitations at play that can restrict the amount of upwards growth. In Mexico City, for example, height restrictions guide the growth outwards rather than upwards, and often the preservation of historic low-rise architecture halts expansion plans. In an attempt to mine the possibilities for alternative expansion, Kurt Kohlstedt from 99% Invisible has presented a round-up of the different ways in which architecture can instead grow below the ground surface.

The New York Lowline. Image Courtesy of NYCEDC

While most cities strive for a sustainable level of urban density, there are limitations at play that can restrict the amount of upwards growth. In Mexico City, for example, height restrictions guide the growth outwards rather than upwards, and often the preservation of historic low-rise architecture halts expansion plans. In an attempt to mine the possibilities for alternative expansion, Kurt Kohlstedt from 99% Invisible has presented a round-up of the different ways in which architecture can instead grow below the ground surface.Real-world concerns such as the cost and logistical nightmares of large-scale excavations ground some of the following proposals, but their provocative nature is opening up the dialogue for future possibilities. Several conceptual new projects, such as a 35-story subterranean "Earthscraper" designed by BNKR Architectura and the recent &q...