The add-on can only be added with a cruise. You can easily do the itinerary yourself. We also did the HOHO like sayhello and it's a great inexpensive way to see the city. We had a day and a half in Barcelona and we were able to explore the Sagrada Familia (bought tickets online), Parc Guell, their Arc de Triomf, parc Ciutadella and their majestic fountain Cascada and Montserrat (booked online). The one place we missed was Montjuic and we plan to go there next year. The flamenco dances can also be booked online. Four days is plenty to see the main sights in Barcelona. It's a beautiful city, IMO.