Photo tour: The world's 25 biggest cruise ships

USA TODAY

Symphony also is home to a massive water slide complex on its top deck called Perfect Storm. Royal Caribbean just began adding water slides to its ships in 2016.  Gene Sloan, USA TODAY

2. Royal Caribbean's Harmony of the Seas. Unveiled in 2016, Harmony is just a tad smaller than Symphony of the Seas at 226,963 tons.  Michel Verdure

Notably, while Allure of the Seas is slightly smaller than Symphony of the Seas and Harmony of the Seas, it can hold more passengers. Its total capacity is 6,780.  Royal Caribbean International

Allure of the Seas features one of the largest theaters at sea, capable of holding around 1,400 people.  Michel Verdure

The massive size of Allure of the Seas and its Oasis Class siblings is evident when strolling through their interior public areas. Each of the ships boasts a multi-deck, mall-like area with shops, eateries and bars called the Royal Promenade.  Simon Brooke-Webb / sbw-photo, sbw-photo

4. Royal Caribbean's Oasis of the Seas. Measuring 225,282 tons, Oasis was the world's largest ship when it debuted in 2009, but it has been surpassed by three newer Oasis Class ships.  Royal Caribbean International

While the tonnage measurement of Oasis of the Seas is the same as its younger sister Allure of the Seas, Royal Caribbean says it is two inches shorter. The slight difference made Allure of the Seas the new world's largest cruise ship when it debuted in 2010.  Royal Caribbean International

Oasis of the Seas has two large rock climbing walls that overlook an outdoor aqua theater.  Simon Brooke-Webb, Simon Brooke-Webb /sbw-photo

Among the most notable features of the Quantum Class is a mechanical arm with an observation pod that rises above the pool deck, offering passengers a bird's eye view.  Roy Riley / sbw-photo

Designed to travel to parts of the world with inclement weather, Quantum of the Seas also is home to an expansive interior pool area.  Simon Brooke-Webb / sbw-photo

7. Royal Caribbean's Anthem of the Seas. Unveiled in 2015, the second ship in Royal Caribbean's Quantum Class series measures 168,666 tons.  Simon Brooke-Webb/sbw-photo

Ovation of the Seas features more casino areas than its Quantum Class sisters in a nod to the specific interests of Chinese travelers.  Michel Verdure

9. Norwegian Bliss. Unveiled in April 2018, Norwegian Cruise Line's largest ship ever measures 168,028 tons.  Norwegian Cruise Line

Built with all the trappings of a major mega-resort, Norwegian Bliss features top decks chock full of pools, water slides and other outdoor amusements.  Gene Sloan, USA TODAY

10. Norwegian Joy. Christened in 2017, the second ship in Norwegian Cruise Line's Breakaway Plus series measures 167,725 tons.  Norwegian Cruise Line

Norwegian Joy was specifically designed for the Chinese market with such features as a tranquil, park-like space at the center of its top deck in lieu of a more traditional pool area.  Gene Sloan, USA TODAY

Norwegian Joy was the first cruise ship with a racing track on its top deck.  Ingrid Fiebak-Kremer

Royal Caribbean's Freedom Class ships including Liberty of the Seas are among more than a dozen Royal Caribbean vessels with a FlowRider surfing pool.  Royal Caribbean International

Liberty of the Seas also offers miniature golf, a staple of Royal Caribbean ships.  Royal Caribbean International

Royal Caribbean's Freedom of the Seas also boasts an ice rink, which offers skate rentals to guests.  Corinne Canning, USA TODAY

15. Royal Caribbean's Independence of the Seas. Dating to 2008, Independence measures 154,407 tons, the same as sister ship Freedom of the Seas.  Simon Brooke-Webb / sbw-photo, sbw-photo

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