Ferry Spain to Italy

Depends where in Italy. Depends how much time you have to be in Italy.

From Barcelona....
Train to Rome....14-15 hours with 3-4 changes.
Ferry to Rome....20 hours
Flying to Rome...Priceless......2 hours

There are some great, short-term cruises that go from Barcelona to Rome (Civitavecchia).

Here's a 3-night one on Norwegian.

Here's a 3-night one on MSC.

Here's a 4-nighter on MSC.

Here's another 4-nighter on MSC with a different itinerary.

We are using a similar strategy next year to get from London to Berlin - taking a 2-night Cunard cruise from Southampton to Hamburg. Very excited about it, as it will be 2 full days of relaxing and fun on the cruise ship, with the added benefit of transport from one place to the next.

https://www.grimaldi-lines.com/en