The Fontana del Nettuno is one of Messina's classic monumental fountains, showing Neptune controlling the sea with figures below him. Its theme fits the city perfectly: Messina has always faced the strait, and the fountain turns that maritime identity into sculpture.
It is a short stop rather than a destination by itself, but it belongs on a waterfront walk with the cathedral, harbour views, and the Strait of Messina. Look for the composition and symbolism rather than expecting a large piazza spectacle.