It's a beautiful, small, walkable, historic city that was appropriately added to the World Heritage List in 1996. Ravenna is near the Adriatic, so 20 minutes from the city, you'll find wonderful beaches. Near the sea means seafood. Yes! But, Ravenna is situated in the region of Emilia Romagna which is known as Italy's breadbasket. So all kinds of food is there to be enjoyed.
One of the most famous residents of Ravenna was Dante who moved there in 1318. He finished Paradiso there and died in 1321. His tomb, where is bones are located (Florence wanted his remains moved there but were refused so only have a monument to their most famous poet), is connected to the Basilica di San Francesco and, as you will see in the photo below, it's a small marble mausoleum at the end of a narrow side street.
Ravenna is best known for its mosaics from the early Christian and Byzantine periods of the 5th to the 8th centuries. The city was actually the capital of the Roman Empire in the 5th century, just before the empire's fall. To feel the full impact of the stunning mosaics, if you can only do one thing in Ravenna, it has to be a visit to the Basilica of San Vitale and Mausoleum of Galla Placidia.
While there are many other options, I'd start my visit of Ravenna at the main attraction, the Basilica of San Vitale and the Mausoleum of Galla Placidia. They are both in the same complex along with the National Museum of Ravenna near the center of the city. Walk from the Piazza del Popolo along cobblestone streets to the entrance of the Basilica. On your left will be the ticket office and entrance to the museum. The Mausoleum is located behind the Basilica.
Open every day of the year except December 25th and 31st, you'll also want to keep in mind that the Basilica is a church. Tours are suspended from 10:00 am to 12:00 pm for celebrations of the Holy Mass every Sunday. The entrance includes a visit to the Basilica of Sant'Apollinare Nuovo, the Neonian Baptistery, the Mausoleum of Galla Placidia, as well as the Archiepiscopal Museum and Chapel.