We did Iceland and Norway a few years ago on Sea Princess and most places the ship docked in town so there was no need for shuttle buses. You don't say where you are going but Reykavick, Akureyri, Shetland, Faroes, Flaam, Stavanger and oslo were all places where we just walked ashore from the ship. We did however go on an excursion in Iceland which took in the Blue Lagoon (although not long enough to swim in it!) but I expect you could do this independently. Hope this helps a bit.