Hi! Dronnygirl
We're also in Ravenna on a Sunday ( August) with Marella Explorer2
There are buses from the cruise port to the town center, near the railway station.
You can take the bus 90 ( stop Porto Corsini) to Ravenna FS if you want to visit the San Vitale basilica and the mausoleum with their mosaics.
As it is Sunday, there's only a bus every hour (8.39 9.39 ....).
You can find more information on the bus website : www.startromagna.com
We're looking forward to this cruise.