We are on the NCL Star as well, departing from Reykjavik May 30, 2024. We too were questioning what to do in the hours before we board. We decided to book the Reykjavik Hop on Hop off Bus for the day. $35.00 per person, it has a stop right in the cruise port and hits all the major sites. It starts at 9:30 in the morning, and the loop takes about 90 minutes. More than enough time to see the main city sites, and be back on the board in time for the 2:00 All Aboard. - Steve