My yoga and fitness teacher just returned from a Viking cruise around Iceland and I talked to her briefly before class today. I was very interested in hearing about Iceland, but unfortunately their cruise was truncated because one passenger (all of whom were fully vaccinated) tested positive several days into the trip. That passenger was isolated, and no other cases were reported. They were initially allowed to leave the ship for excursions, but the buses were called back before they reached their destination, and then the ship was ordered to return to Reykjavik a day early. They got free drinks on the last day, but one margarita was enough for her, and did not make up for all they missed.
She did not have time to tell me more than that, so I looked it up and found this detailed report from another passenger:
The lesson to be learned, I suppose, is that one needs to be very flexible and “go with the flow” when traveling these days.