We spent the day dancing, relaxing, and swimming in the sea. We got lucky because it wasn't too windy, so no one got seasick.
We booked through Charter System Yacht. It cost about €120 per person. This was the cheapest we could find for 10 people, and it was definitely worth it. Our captains were extremely nice and made sure we were all having a good time. The company also provides towels, food, drinks, snorkeling gear, and pool noodles. They took us to a super pretty swimming spot, and we spent so much time in the water. They also did a great job taking videos and pictures of everyone, so we were able to just enjoy the day.