Abstract: The Jamsu (Haenyeo) are female divers on Jeju Island, South Korea, who catch marine animals and harvest seaweed through breath-holding diving. Responding to the ebb and flow of the ocean, they have cultivated both sea and land, connecting these ecologies by transferring necessary nutrients from one to the other. Based on a year-long landscape fieldwork in the Jamsu community by the lead author (Kang), this research proposes Submersible Urbanism: a rhythmic, reciprocal, and regional system in which actors positively exchange their (by)products through the cultivated land/seascape and built environment. This paper provides three propositions of Submersible Urbanism in the scales of city, landscape, and architecture: a cyclical trophic system across the island and sea, submersible walkway, and a new commons for the expanded Jamsu community. These propositions of Submersible Urbanism suggest a resilient model of living in the era of climate change and sea-level rise.