We did the "Dubrovnik at Leisure" tour through NCL. Do NOT do this excursion. You essentially pay $80 for a $15 shuttle. We booked this tour because we thought it was different than the shuttle. It was complete chaos when we got off the ship and they had the people on our tour and the people who needed to buy tickets for the shuttle, wait in the same line. So we didn't even get on the shuttle ...
Definitely a highlight of the Cruise. We went on a Viking included tour of the medieval city in the AM, went back to the ship for lunch, then returned via complimentary shuttle bus to climb the walls of the city on our own. One of the most scenic & memorable experiences of the trip! ...