I’m currently in a Mediterranean cruise, which wraps up tomorrow. Our route was Athens > Santorini > Kotor (Monte Negro) > Messina (Italy) > Naples > Barcelona.
This was my first cruise ever and my general recommendations are to book tours at each stop, and arrive a few days early to enjoin your starting destination. We spent 2.5 days in Athens. Regarding the excursions you get a lot more information with a tour guide, and don’t have to stress out about how to get places and back to the ship in time etc. We did it both ways and the stops where we booked excursions were much more enjoyable. Now to specifics.
Santorini: A bit overrated for me, but was still fun. Going from tip to tip on the island is probably a 30-40 min ride. We had an excursion booked this day. First a bus took us to the south tip of the island where we visited Akrotiri, which is an archeological site. I highly recommend a stop there if you enjoy history. After that the bud took us all the way north to Oia, which is the famous place with the blue domes that you probably see everywhere. Bud dropped us off and we had 3 hrs to walk around. We got lunch first, which was a good thing since it took 1.5 hrs to eat. We picked a restaurant on a parallel road to the main road. Food was amazing, but they were a bit understaffed. Also, drank a local beer called yellow donkey, which was a good light beer and refreshing given the hot weather. After eating we cruised around the shops, and then took our pictures by the famous blue domes. After that the bud drove us back to the center part of the island and dropped us off. The middle island is the larger portion and more city like. Here we could explore it on our own or get back to the boat. At this point we were kind of tired, so went to a roof top bar and enjoyed some wine before taking the cable car back down to the water shuttles to the ship.
Naples: Highly recommend going an a guided tour of Pompeii. This is what we had planned and what I was looking the most forward to during our cruise. My wife is currently on her first trimester of our first pregnancy, and unfortunately we had a bit of a scare as we were porting in Naples. Ended up spending all day in a local clinic for a ultrasound and some check-up. Thankfully baby and wife are fine, but as you can guess we were not able to make it to our excursion.
Ultimately have fun and relax! Almost forgot, but on port days try to wake up early to see the ship porting. Usually stunning views during sun rise!