Arena di Verona is the second biggest amphitheatre in Italy after the Colosseum in Rome. They usually have different concerts and operas held there which are supposed to be a great experience to attend. You are able to visit inside during the day and I highly recommend you do! A good tip is to do it on any first Sunday of the month because then you only pay 1€/person, when the normal price would be 10€ which still isn't much if you're visiting any other day.