With more than 9.4 million people living in the capital city sprawling 605 square kilometers, Seoul is one of the most crowded cities in the world. It boasts a population density of some 15,567 people per square kilometer. New York City, by comparison, has a population density of about 11,313 people per square kilometer. It comes as no surprise that in Seoul, where space is scarce, we build not only above ground and ...