With the clever use of design elements, Queen Mary 2, the largest passenger liner ever built, bears a striking external resemblance to the smaller, older Queen Elizabeth 2. The world's grandest and most expensive liner is something of a transitional ship, incorporating classic ocean-liner features -- sweeping staircases, soaring public rooms, a 360-degree promenade deck, and a grand ballroom -- all comfortably within a hull that also includes a trendy Canyon Ranch Spa and a full-scale planetarium.