The Republic of Rose Island was the name given to an artificial platform of 400 m² that stood in the Adriatic Sea outside Italian territorial waters, designed by engineer Giorgio Rosa in 1958 and completed in 1967.
This episode is also available as a blog post: https://weirditaly.com/2021/08/06/the-curious-history-of-the-republic-of-rose-island-a-micronation-on-a-man-made-platform-off-the-coast-of-italy/