I just went on my first cruise and I booked the Blue Lagoon Excursion ahead of time and when we got on the ship, our tickets were in the cabin. The excursions only allow a certain number of people so if it's a popular one, you'll want to book it in advance. Some people booked the tour to Atlantis. I wanted to see it too but didn't want to pay the big price tag. I found out on-line that it's free to go in and look at the aquariams and all so we just paid for a taxi to take us there. I would just research the areas you are going and see what your options are.