Harmony of the Seas: What you need to know about the world's biggest cruise ship. Everything YOU need to know about $1billion boat Harmony of the Seas. Introducing the Harmony of the Seas® - the newest addition to Royal Caribbean's award-winning Oasis Class fleet. The world's biggest ship with the world's best features just got even better. There's no turning back once you take the plunge 10 stories into the mysteries of the deep on the tallest slide at sea, Ultimate Abyss, as well as the exhilarating multilevel Perfect Storm slides. We've also reimagined and enhanced the unique experiences that have made Royal Caribbean the best cruise line overall 12 years in a row. As the kids explore Splashaway Bay, take a tree-lined stroll through Central Park, or find your own haven in any of the other seven iconic onboard neighborhoods. Sip a post-dinner cocktail crafted by a robot in our unique Bionic Bar, or sit back and watch for the first time at sea, Broadway's hit Musical Grease. Share every moment with not just family onboard, but friends back home with VOOM - the fastest Internet at sea.