Beauty is surely in the eye of the beholder and thus there can be no specific No 1. Answers already recorded prove this as all are truly beautiful in their own but differing ways. Scandinavia, UK, France, Iberian Peninsular, Australia, New Zealand etc, etc amongst others all have coastlines in places that take the breath way. The most beautiful will differ according to the observer and maybe the time or circumstances obtaing at the time of viewing to the individual. As an individual myself, I could not nominate one single coastline for fear of betraying another. At the same time, those who nominate specific coastlines provide impetus to visit those indicated that, as of yet, ve not been viited by myself.