This beautiful card is from - you may have guessed already - Napoli. The piazza del plebiscito sees a lot of visitors particularly at nighttime. The church with the large cupola on the right is called San Francesco di Paola. You can see the Mediterranean Sea in the back and the Vesuvius would be on the left if the card was even wider.
The stamp is from the national instruments series and shows the launeddas, a Sardinian woodwind instrument.