The last of Royal Caribbean International’s five Voyager-class ships — all designed to carry 3,114 passengers — Mariner of the Seas was the first (in 2012) to get the Royal Advantage upgrades that will eventually give the entire fleet the signatures of Oasis-class ships. That means its 15 decks are packed with activities (rock-climbing, ice and in-line skating, minigolf, three pools, six hot tubs, and a poolside movie screen), along with eight dining venues, 17 bars and lounges, and the family-friendly DreamWorks Experience. Yet despite its size, Mariner of the Seas never feels crowded.