Millions of tourists visit Asia each year for its pristine beaches and cultural treasures, but Nick Bonner offers travellers something different: the "socialist paradise" of North Korea.

Bonner launched Koryo Tours in Beijing in 1993 along with a few colleagues, taking an initial group of 12 curious tourists keen for a glimpse inside one of the world's most isolated countries.

That grew last year to 1,300 hardy travellers, who take in such unconventional tourist sites as a former sanatorium, a seafood processing plant, and a "model collective farm," said Bonner, a former landscape architect.

"Most people we take in are not the sort of people who would normally travel on group tours. For us, it is important the person has the best experience possible," Bonner told AFP in an interview at his offices in Beijing.

It was just that for British chemical engineer Dennis Murphy, who was impressed by being treated "almost as an official visitor" on a trip he called "magic... an entry into a totally different world."

North Korea has only been open to Western tourists since 1987 and remains tightly controlled. Koryo clients are accompanied by North Korean minders at all times and independent wandering is forbidden.

Foreign journalists are not allowed on the tours, and American tourists are still banned from exiting North Korea by train to China -- the North's main link with the outside world.

Initially, Koryo Tours could only bring its clients to Pyongyang, the Demilitarised Zone on the border with South Korea and Mount Myohyang, said Bonner, who opened the first live music club in Beijing in the early 1990s.

"Slowly we have been getting more and more access," the Briton said of his tours, which bring in roughly half of foreign tourists to North Korea in partnership with the state-run Korea International Travel Company.

"It has been amazing, based on trust."

North Korea is desperately poor after decades of isolation and bungled economic policies. Huge numbers of its estimated 24 million people suffer inadequate nutrition, aid agencies say.

That is a side of the country tourists do not see, but the door is slowly opening.

With the help of 40 local multilingual tour guides, Koryo's offerings have expanded to include the "tranquil beaches" of North Korea's coasts, and even home stays in the town of Haeju and the industrial city of Chongjin.

Tours also go to the South Korean-funded joint industrial estate in Kaesong, the port city of Nampo, and Mount Paekdu -- a sacred site for North Koreans near the birthplace of leader Kim Jong-Il previously closed to Americans.

In September, Bonner will achieve a first -- taking foreign tourists on a bicycle trek near Mount Paekdu.

"That had never been done before -- it's a challenge," Bonner said.

In Pyongyang, women are not allowed to cycle as it is viewed as "inelegant... and dangerous," Bonner said.

Also on the tourist trail is the country's second-largest city Hamhung, open to foreigners only since last year, and Rason, a rarely-seen "free trade" area.

One trip is centred around March 21, the day personal income tax was abolished in the Stalinist country, while another offers the chance to "relax in a former sanatorium on the east coast."

But the real prize is a visit to the Arirang Mass Games -- the world's largest choreographed display of synchronised acrobatics, dance and flip-card displays, involving up to 100,000 people.

"The most spectacular event on Earth... a performance... which is only possible in North Korea," a Koryo brochure says of the next festival in August.

Trips to North Korea are not cheap. A four-night stay can run about $1,400 a person.

The cost helps Bonner to fund another venture -- making documentary films in the country, which in the past have been shown at the Sundance Film Festival in the United States.

Tony Yoo, an Australian, said he was struck by "the severe isolation of the country and the deprivation of liberty, even for foreign visitors."

Some wonder if the tourist dollars support a regime universally condemned for rights abuses, but Greek traveller Peter Psiachos said it could help coax North Korea out of its isolation.

"It would make people there less fearful of outsiders and further educate us that North Korea is not the enemy," Psiachos, a lawyer who lives in New York, told AFP.

Australian teacher Lachlan Olive visited North Korea in October, expecting "drab, heavily polluted" scenes, but was surprised by the number of parks and greenery in Pyongyang, and the quality of its infrastructure.

But he wondered whether, on a visit to a modern collective farm supposedly visited repeatedly by North Korean leader Kim Il-sung, he was seeing the real North Korea.

"We also visited an orphanage that had a similar feeling of being 'sexed up' for our benefit," he said.