2017 promises to be a year of superlatives: the industry is expecting some 25 million sea cruise bookings worldwide. That would be a million more than in 2016. In addition, some 26 new cruise ships will be embarking on their maiden voyages. That will bring the total number of cruise ships sailing the seas and rivers to 474.

In the past, 1,000 passengers was regarded as a lot, but today, 4,000 is fairly common. It's become mass tourism on the sea - and people love it, most of all the US Americans, who top the list of cruise holidaymakers, followed by Brits and Germans.

66 meters (217 feet) across, over 362 meters long, 16 decks and room for 5,400 passengers and 2,000 crew members. Added to that are 20 dinning rooms, 23 swimming pools and a park with more than 12,000 plants: the "Harmony of the Seas" is currently the largest cruise ship in the world.

You won't find pictures like this in a brochure. For years, environmentalists have criticized the high pollution emitted by these ocean giants. They are demanding the use of liquid gas instead of crude oil and for exhaust filters to be installed. The Norwegian Cruise Line has announced that in 2017 their new vessel, the "Norwegian Joy" will be equipped with the biggest filter-system in the world.

Cruise ship holidays are losing their just-for-the-old image. Every year, the average age of passengers sinks by one year, so it currently stands at 50; on modern vessels it is a lot lower. But whether young or old, single or family, culture fan or party animal - there is always a suitable cruise ship to meet the demand.

This is a special event for the young or those young at heart: since 2011, there has been the "70,000 tons of Metal" festival, which was sold out once again this year. The "Independence of the Seas" sailed from Florida to Haiti. On board were 60 bands and 3,000 heavy metal fans.

Swimming pools, discotheques, casinos and theaters are very much basic equipment for modern cruise ships. In order to gain entrance to the fleet of superlatives, you need a little more: a kart track, ice rink, skydiving, climbing-course, IMAX-cinema, rafting or surfing, like here on the "Quantum of the Seas."

With so much entertainment, nature tends to be relegated to being a side feature - but not always. The choice of route is as important as the choice of vessel. Sea cruises to the Caribbean and the Mediterranean are still the most popular destinations. On the other hand, a tour to the eternal Antarctic ice is a very exclusive experience.

As passengers are on average younger, a more relaxed atmosphere has become established on board, so that often black tie and gowns are no longer an obligation. That is apart from sophisticated ships like the "Queen Elizabeth." Should passengers not have the appropriate clothes with them, the "Royal Arcade" will help them buy attire acceptable to British tastes.

The first to be fully booked are not the cheaper interior cabins, but rather the expensive suites with sea views. No one wants a sea cruise in a shoe box. The design of the new vessels takes this into consideration - some ships have done away with inside cabins altogether, while others install virtual balconies that simulate a sea view in real time.

Whether in London, Marseilles or Miami - sailing into port is always a special highlight for most passengers. Once on land, the passengers separate according to interests: sightseeing and shopping or visits to the museum and a musical show - either way, it gives them a break from the daily routine on board the ship.

On land there is more action to be had: bike tours, diving courses, desert safaris, swimming with dolphins, wilderness hikes, motorbike, segway and quad-bike tours - all of which promise a lot of fun. However, these do tend to come at a price - these additional expenses on a sea cruise are not to be underestimated.

Those who can't afford to go on a sea cruise can at least enjoy taking a look at the vessels! Like, for instance, in September during the Cruise Days in Hamburg. That's when 10 sea cruise ships will be docked in the harbor, more than ever before. How appropriate for a year of records!