The world's last true ocean liner docks down under

Despite its looks, the Queen Mary 2 is no cruise ship.

The world's last true ocean liner has moored in Sydney on its 108-day round-the-world voyage.

A Concorde for the Gilded Age, the ship was built for zipping passengers back and forth across the seas on a tight schedule.

"We leave Southampton at four o'clock, and seven days later we arrive into New York at seven o'clock in the morning, no matter what the weather," the ship's captain, Tom Connery, told AAP.

Queen Mary 2 was once the largest passenger ship, taller than the Eiffel Tower if balanced on its end. Today, it's a minnow.

The current titleholder, Icon of the Seas, with 28 restaurants, a laser tag arena and a water park, is almost twice as heavy and 19 metres longer.

And its big sister is set to launch in 2026.

Short on water slides, Queen Mary 2's nostalgic operator Cunard instead invites passengers to savour the world's largest seaborne ballroom and take British afternoon tea every day.

And the ship trumps its rivals in another category:

"It's designed for speed," Capt Connery says.

"The ship's hull has extra steel, powerful engines and a wide beam to cut across the North Atlantic."

In 2024, it celebrated its 400th voyage between Southampton and New York and on its current trip Capt Connery has again been putting the hammer down.

Departing England on January 11, Queen Mary 2 will rocket back home to Southampton by April 30.

In Sydney on Wednesday, those on board were asked to indulge in another anachronism: letter writing.

When it departs on Thursday, Queen Mary 2's passengers can busy themselves answering some of the more than 500 letters sent by Australians as part of a campaign to encourage more thoughtful and profound connection.

While Australia Post in February reported a bleak outlook for letter volumes, Leah Mano from pen-pal matchmaker ConnectedAU sees renewed interest in slow and intentional communication.

"We know that one of simplest but most powerful ways to create connection is just to write a letter," Ms Mano said.

"This isn't about nostalgia, it's about depth."