It was, with no exageration, PERFECT !! This place is to die for, especially the terrace. It feels amazingly like home. It's comfortable, clean, beautiful, well equipped, a few steps from the nice streets of historical centre with amazing things to visit and also with restaurants, pizzeria, gelateria, pasticceria. There's a supermarket downstairs as well which is really practical to have "apéritif", dîner and breakfast on the beautiful terrace of the apartment. It's not far by foot (15 minutes) from the ferry port if you want to go to islands near Naples (Capri, procida, Ishia)
And last, but not least, Diego and Roberta are really easy to communicate with. They were so helpfull and nice. I highly recommend this place for a stay in Napoli.