You could nuke the Straits of Gibraltar from below the water to create a crater that formed a double dam, closing the Mediterranean sea for the water levels to

You could nuke the Straits of Gibraltar from below the water to create a crater that formed a double dam, closing the Mediterranean sea for the water levels to rise and to flood all the coastal cities. Admittedly the nuclear weapon would have to be pretty big but the USA has thousands of the things as does Russia. So as we speak, right now, and for the last few decades, you could say that the area already is 'the biggest soft target'.