Material expressions of emotion and ideology transformed downtown Seoul from 2014–2019 into an extended commemorative monument dedicated to those who died in the tragic sinking of the ferry Sewŏl on April 16, 2014. This unfortunate event stimulated diverse personal and political responses, in large part because there were 250 high school students on a fieldtrip among the 304 casualties. Analyzing the new shapes that the Sewŏl memorials have introduced into the urban landscape reveals the ways in which the city has maintained its fast flow of life while at the same time allowing city dwellers to poetically express grief, anger, and hope. The aggregated practices of various people with diverse agendas amounted to unique artistic, architectural, and emotion-soliciting structures that are delineated in this essay as landscapes of mass cooperation. These landscapes were crafted by thousands of individuals without a firm aesthetic or content related scheme, and they changed as emotions shifted from hope for survivors to grief over the immense death toll and rage toward those responsible for it.