Abstract — In this paper, I discuss the main arguments that deal with the issue of high density and utopian architectural projects to investigate the advance of megastructure buildings and artificial land concepts in Seoul during the 1960-70s. It is my purpose to highlight the architectural influences that have generated these ideas by pointing to the genesis and the evolution of critical projects in Seoul. The paper is structured as follows. After giving an overview of the scope of the contemporary high-density urban factors, I review the particular evolution of the megastructure projects from the 1950s. This analysis creates the background to introduce South Korean projects that have been influenced by the international concepts of utopia. The main case study is the Sewoon Sangga building and its strictly related synergy with the highly productive surrounding area. The results of this research have advanced the ground for further investigations on the evolution of megastructure projects and their influence on the surrounding urban environment. The clash between formal and informal architecture is particularly accentuated in Seoul as the high-density condition of this megacity generates situations that reflect both the traditional milieu and the technologically advanced environment.