When it was completed in 2003, the Queen Mary 2 was the world's largest passenger ship. It has since been surpassed in size by a number of other cruise ships, but it's still the largest ocean liner ever built. (Unlike the QM2, a normal cruise ship is not designed to make transoceanic voyages.)
The QM2 is so tall that it had to be built with a shorter-than-usual funnel so it would be able to pass beneath the Verrazano-Narrows Bridge and enter New York Harbor. It's still a tight fit (video); at high tide, the ship has only 13 feet of clearance beneath the Verrazano.