Rhapsody of the Seas and Splendour of the Seas to Join Allure of the Seas to offer Unmatched Europe Vacations Only Found on Royal Caribbean. For nearly five years, Oasis of the Seas and Allure of the Seas, sister ships that share the title of the world’s largest and most innovative cruise ships, have taken more than two million guests to unforgettable Caribbean destinations. Royal Caribbean International has announced that, for the first time since the ship was delivered in Turku…