After almost a decade of travel, a Danish man has become the first person to visit every country in the world in an unbroken journey without flying.

44-year-old Torbjørn "Thor" Pedersen set off in October 2013 on an ambitious mission he expected would take four years.

He arrived at his 203rd and final country - the Maldives - on board a container ship on Tuesday, marking the end of a 3,512-day adventure.

"In a way, this has just been a huge sociological experiment and a success at that," Mr Pedersen told the ABC.

"Because I cannot remember a country I've gotten to where I did not receive some sort of kindness or support from people."

The United Nations recognises 195 sovereign states - but Mr Pedersen has included other disputed territories in his tally.

He spent at least 24 hours in each country, travelling by foot, car, bus, train and boat - including 37 container ships.

"At this point, for me, getting on board a container ship is not much different from getting onto a city bus," he laughed.

"I rank among the 150 most-travelled people in the world."

Mr Pedersen said while others had visited every country using planes, or broken up the journey by flying home and later resuming it, he was the first to do so entirely without flying and in a single, continuous voyage.

The project - dubbed Once Upon A Saga - has been tested by bureaucratic and logistical issues, civil unrest and unexpected hurdles like the Ebola outbreak in West Africa.

"This is something which has never been done before, so it has been hard to foresee everything that would be coming my way," Mr Pedersen said.

"I am proud that I never gave up throughout all of this. I am proud that I was able to show the strength that was required."

The traveller was stuck in Hong Kong for two years during the COVID-19 pandemic and considered abandoning the project.

"This was before we had the vaccines, we didn't know where it was heading, we didn't know how dangerous it was. And it was just taking up more and more time," he said.

While his plans were paused, Mr Pedersen married his long-term girlfriend Le, who visited him 26 times throughout the project.

When the world opened up again, he took a ship to Australia, arriving at the Port of Townsville in April 2022 and staying in the country for almost two months.

His budget for the project was just $US20 a day, financed through personal savings, corporate sponsorships and crowdfunding.

Tens of thousands of people have followed his journey on social media.

"Every time I look at a world map now or a spinning globe, I'll look at it and I'll think, there's someone kind and helpful in each and every one of those countries, and I came across them - and what are the odds of that?" he said.

After starting out his travels "starry-eyed", Mr Pedersen said he finished the mammoth journey feeling "exhausted, especially mentally".

"Although there has been a lot of pain and disappointment, there has just been a great deal of knowledge and beauty and great experiences throughout all of this," he said.

He believes his achievement - reaching every country in a single journey without boarding a plane - might never be done again.

"It got harder as I went along," he said.

"More and more ferry connections disappeared and were replaced by aeroplanes, I think border crossings got far more strict, and it's getting almost impossible to come on board container ships as a passenger."

After spending some time unwinding in the Maldives, Mr Pedersen will return home to Denmark for the first time in nearly a decade - also without flying.

"Once I'm home, it's going to be about friends and family, and also just taking a deep breath and realising that [I'm breathing] Danish air for the first time in a very, very long time," he said.

"And who knows, it might not be too late for my wife and I to start a family, so if we can get that ball rolling as well, then there's an adventure hidden somewhere within all of that."

Mr Pedersen has spent the past four years working on a feature-length documentary and plans to publish a book about his travels.

He also wants to get back into marathon running and participate in races across the globe.

"It's a lot easier to deal with running for four hours than it is to go through 203 countries over nine years and seven months - but I do see the parallels," he said.