The emerging part of the submerged pavilion designed by Renzo Piano for the Genoa Aquarium in the basin of Porto Vecchio is a slender, transparent walkway over the water, just three metres high and 30 metres long; it is bordered at each end by small towers and is located between the main museum building and the Grande Nave Blu [Great Blue Ship] of Biodiversity. Visitors can observe the evolution of the dolphins through the uninterrupted windows along the waterway and continue exploring the exhibition pool in an underwater tunnel. Built in the shipyards in La Spezia and Voltri, the amphibious building was towed here; to be able to face such conditions, the steel and glass structure had to be special: resistant to the aggressions of the sea, light and not too bulky for transport whilst also being strong, secure and able to house the public. Slim, essential, robust and inalterable, the OS2 65 steel profiles, which were also used for the emergency exits, passed this test with flying colours.