Updated October 2, 2017
A sea day on a cruise is a day during which the ship does not stop at a port. Sea days are frequently included in itineraries where the ship must travel long distances between ports of call. They are also common on the schedules of mega-ships, which have a limited number of ports they may enter because of their enormous size -- and enough activities to keep cruisers entertained onboard. Sea days may be listed on the itinerary as "cruising" or "at sea."
Days at sea are more common on Caribbean sailings than on Mediterranean or European routes, where destination ports are generally closer together. Multiple sea days are always part of the schedule for repositioning cruises like those that cross the Atlantic or Pacific oceans, and Alaskan cruises often include a day of scenic cruising in the Inside Passage.
It is also common for a ship to replace a port of call with a day at sea in the event of weather or sea conditions that make docking the ship or operating tender boats hazardous.
Sea days are usually loaded with scheduled activities throughout the ship. Events like cooking demonstrations, educational lectures, poolside games, dance classes and movies make sea days anything but boring. Often, formal nights are held on a sea day, so passengers have plenty of time to primp or go to the ship's salon before dressing up for dinner.