We have already seen Santiago de Compostela a few years ago. If we take a cruise visiting Vigo and Corona, what is there to see in that area?
Vigo isn't a huge tourist destination. But, we spent a few days there a couple of years ago. You'll find lists of things to do on expedia and other places online. We were there in late June and found it perfect for temperature. I'd say that that my highlights were the food (lots of seafood), and the Cies Islands - I think about 30 mins ferry ride from the city. Feels like the Caribbean sea beaches - but the water is chilly.
We liked it there a lot. We took day trips to Valenca Portugal, Ourense, and Pontevedra. It's a really pretty part of Spain (but I've yet to find a part of Spain that's not pretty).
As a day trip, Lugo might interest you. It’s 49 miles from A Coruña. The town itself is small and can be seen in a day. The main draw is the UNESCO world heritage site Roman wall that encircles the town. If I remember correctly the walk along the wall is about 2.4km. The cathedral is nice to visit, but is like so many others in the country. Closer to A Coruña is Betanzos. Another small town whose main draw are the glass enclosed wooden balconies common in Galicia. Many can be seen from Praza Irmáns García Naveira in the center of town.
If you had a rental car and more time, there are some nice views from Cabo Ortegal in the north and a very scenic beach just west of Ribadeo at As Catedrais beach. Not certain about now, but there used to be wild horses that hung out near the lighthouse at Cabo Ortegal. Both are fairly remote and the roads getting to them are the most rural or rural roads in Spain. Due west of Santiago de Compostela on the coast is Muxia. Very scenic rocky beach and small chapel. What I’ve found common in many of the small towns and countryside in that area are wayside crosses, granaries (horreos), and small chapels, but no major draws. Most can be seen in less than an hour.
Edited: Leon is 152 miles from A Coruña and too far away for a day trip. It is a nice city worth a couple days.
We picked up our rental car in Vigo and headed to seaside Baiona. There is a model of the La Pinta, one of Columbus’ ships, which returned there from the trip to the New World. We spent several days at the Parador there . Fabulous seafood in town.
On the other hand, I could never see enough of Santiago de Compostela.
Have you visited Leon and it’s Gothic cathedral with spectacular stained glass windows?
Rias Baixas, town of O Grove.
A favorite area of Spain for us.
While Vigo isn't a bad place, it has only the tiniest imaginable historic district and is the dullest city I've seen in Spain. I'd definitely head out of town. I enjoyed all of these places in that part of Galicia, and I reached them via public transportation:
Pontevedra: a city of some size located north of Vigo, with which it has good transportation links. Known for comparatively nice weather in a part of Spain that tends to be very overcast. Pleasant historic area, though not the most distinctive I've seen.
Tui: A small town on the Portuguese border (across from Valenca) with an evocative, relatively non-touristy historic area; the cathedral has an English-language audioguide. Transportation is probably rather infrequent. (A Google search for photos seems to deliver a lot that are outside Tui.)
Cambados: A small coastal town with attractive architecture. Beyond Pontevedra. Mostly flat as the proverbial pancake. Beyond Pontevedra.
Combarra: An atmospheric coastal town, quite touristy. A bit of uphill/downhill walking here, but I think most people would find it visually more interesting than Cambados--thus the tourist shops, etc. Beyond Pontevedra but very close to it.
A Coruna I liked a lot. You may not need to leave that city at all. If you want to branch out, I can second the recommendation for Betanzos. There was more to see there, just walking around, than in the smaller Combarra and Cambados. The town is quite hilly as I recall, and I don't remember much cover should your day be rainy. Betanzos is close to A Coruna, so you could see some of both places during your port call.
I spent a day in the Cies Islands. I don't recommend them for the typical traveler, and I know you share my view that European beaches are most often less than exciting to American visitors. The best I can tell, the Cies Islands' main claim to fame is that there are lightly visited, sandy beaches. It's understandable that they would be highly rated by Europeans, but for most American tourists with limited time in Europe, it's a different story. They maintain the quality of the Cies experience via capacity controls on the ferries heading there from Vigo. It is sometimes necessary to buy your ferry tickets a day ahead of time, and as of 2016 it was always necessary to buy a round-trip ticket. There are two ferry companies serving the islands, but you could not mix and match their departures, nor could you wait until you reached the islands to select the time of return.
I haven't been to Lugo, so my failure to mention it here should not be interpreted as a negative opinion. I did like Leon a lot. In addition to the cathedral, the historic center is nice (though full of bars and restaurants), and there's a Gaudi building you can visit. However, the best I can tell from a quick internet search, Leon isn't a viable day-trip by public transportation from either Vigo or A Coruna, and it would also take too long by car, at least 6-1/2 hours round trip from A Coruna.
If you do make it to La Coruña, make sure to check out the Tower of Hercules, the last standing ancient Roman lighthouse in the world and modeled after the Great Lighthouse of Alexandria. Located just outside the old town on the peninsula.
In between La Coruña and Vigo is the Castro de Baroña, the stunning ruins of an Iron Age fortified Celtic settlement, located right on the rugged coast. Just south of Vigo is the equally stunning Castro de Santa Trega, another impressive ancient Celtic site located on a commanding hilltop.