If this ship’s 984-ft. go-kart track, the longest at sea, sounds like something a kid might concoct, that’s because it is: the idea originally came via the grandchildren of Frank del Rio, CEO and president of Norwegian Cruise Line Holdings. But this $1 billion, 4,000-guest ship, which took its inaugural journey to Alaska in June, offers attractions that cater to adults too, including an onboard casino and a 20,000-sq.-ft. observation lounge. —Alejandro de la Garza