Nomon-yu sits at the southern tip of the Nagasaki Peninsula in the Nomozaki district, home to an exceptionally rare natural high-concentration carbonated spring. The carbonic acid content exceeds 1,000 ppm, ranking among the highest in Japan, and the water also contains approximately 176 mg of metasilicic acid, a mineral prized as a natural skin conditioner. The spring is classified as an iron-bearing carbon dioxide-magnesium-calcium-bicarbonate spring, a remarkably unusual carbonated source for a coastal location. From the main bath, guests enjoy panoramic views of the Goto Sea and the UNESCO World Heritage-listed Gunkanjima (Hashima Island). The recommended bathing method is alternating between the cool 31-degree carbonated pool and the heated baths, a practice said to stimulate the autonomic nervous system and deepen relaxation. The waters benefit high blood pressure, arteriosclerosis, chronic dermatitis, cold sensitivity, and fatigue recovery. The upper floors house Ocean Resort Nomon Nagasaki, where every room offers a view of Gunkanjima.