Pyongyang, North Korea (CNN) Won-moon Joo, 21, smiled and seemed relaxed as he walked into a conference room at the Koryo Hotel in Pyongyang.

Our North Korean government minders informed us Monday night that we'd be interviewing Joo, a request we made on Saturday, just hours after arriving in the country.

CNN was given exclusive access to the South Korean citizen, who is a permanent resident of the United States and has been detained in North Korea since last month.

Joo was most recently living in New Jersey and studying at New York University. He took a semester off to travel across the United States and says he went to North Korea after an unsuccessful attempt to find work in California.

Joo didn't seem alarmed that he could be facing serious charges and prison time for illegally entering North Korea through China.

"I'm willing to accept any punishment," Joo says.

Photos: Invited back to North Korea HERE: Junior Lt. Colonel Nam Dong Ho speaks with Will Ripley, who was granted rare access to the DMZ on Monday, May 4, 2015. CNN correspondent Will Ripley and photojournalist Brad Olson traveled to North Korea after the regime offered them a surprise invitation to return to one of the most mysterious countries on earth. They aren't sure why the invitation was offered, what to expect, or even how long they'd be there. Check out the pictures they've taken to document their journey.Junior Lt. Colonel Nam Dong Ho speaks with Will Ripley, who was granted rare access to the DMZ on Monday, May 4, 2015. Hide Caption 1 of 18 Photos: Invited back to North Korea Junior Lt. Colonel Nam Dong Ho is part of North Korea's standing army of more than one million. An estimated three quarters are based near the heavily fortified border, which has been a flashpoint for violence at times. Hide Caption 2 of 18 Photos: Invited back to North Korea The view from the North Korean side of the DMZ, with armed DPRK soldiers standing guard. Hide Caption 3 of 18 Photos: Invited back to North Korea North Korea displays the armistice agreement that ended the brutal fighting of the Korean War in 1953. Hide Caption 4 of 18 Photos: Invited back to North Korea Two women share a bicycle as they head south on a highway leading from Pyongyang to the DMZ. Hide Caption 5 of 18 Photos: Invited back to North Korea Rebar rises from a building under construction in Pyongyang, the capital city of North Korea, on Sunday, May 3.

Hide Caption 6 of 18 Photos: Invited back to North Korea The Pyongyang Gold Lane, a bowling alley in the North Korean capital, is popular among young people.

Hide Caption 7 of 18 Photos: Invited back to North Korea A life-size statue of late leader Kim Jong Il stands at the entrance to a new water park in Pyongyang. Visitors bow to pay their respects. Hide Caption 8 of 18 Photos: Invited back to North Korea Pyongyang residents play table tennis at a water park in the North Korean capital. Hide Caption 9 of 18 Photos: Invited back to North Korea Kim Jong Un personally inspected the plans for this new water park 113 times and had his top officials safety test the water slides.

Hide Caption 10 of 18 Photos: Invited back to North Korea Pyongyang women wear their Sunday best, including ornate umbrellas to shield themselves from the sun. Hide Caption 11 of 18 Photos: Invited back to North Korea Twin statues honor the late leaders of North Korea Kim Il Sung and Kim Jong Il. Visitors are routinely taken here to pay their respects and lay flowers at the statue, Saturday, May 2, 2015. Hide Caption 12 of 18 Photos: Invited back to North Korea CNN correspondent Will Ripley and photojournalist Brad Olson take a selfie shortly after landing in Pyongyang on May 2. Hide Caption 13 of 18 Photos: Invited back to North Korea The modern new terminal at the Pyongyang airport is nearly complete after an extended period of construction. Kim recently conducted a field inspection of the terminal. Hide Caption 14 of 18 Photos: Invited back to North Korea Air Koryo has an aging fleet, although it has purchased some newer aircraft in recent years.

Hide Caption 15 of 18 Photos: Invited back to North Korea The flight attendants on Air Koryo serve refreshments as monitors show a North Korean televised concert mainly featuring patriotic songs about the military. Hide Caption 16 of 18 Photos: Invited back to North Korea The in-flight magazine on North Korea's only airline, Air Koryo, features multiple pages of Supreme Leader Kim Jong Un. Hide Caption 17 of 18 Photos: Invited back to North Korea The in-flight meal on Air Koryo is a burger and a glass of North Korean beer. Hide Caption 18 of 18

Over barbed wire, through farmland

Joo says he crossed into North Korea near the Great Wall of China in Dandong, an area near the border that offers views of the reclusive nation, which tightly controls access for foreign visitors.

He says he crossed two barbed wire fences and walked through farmland until he reached a large river. He says he followed the river until soldiers arrested him.

"I wanted to be arrested," he says.

North Korea calls itself the DPRK, or Democratic People's Republic of Korea.

"I thought that by my entrance to the DPRK, illegally I acknowledge, I thought that some great event could happen and hopefully that event could have a good effect on the relations between the north and [South Korea]," Joo says.

Joo says he wasn't sure what kind of great event could happen due to his actions.

Joo says he crossed into North Korea near the Great Wall of China in Dandong.

"I hope that I will be able to tell the world how an ordinary college student entered the DPRK illegally but however with the generous treatment of the DPRK that I will be able to return home safely," he says.

Joo says it was, in part, curiosity that led him to North Korea. He said he'd been thinking about making the trip since February.

"Once the thought of entering the DPRK seeped into my mind, I couldn't really escape it. I guess I constantly thought about it," he says. "I thought that as an American permanent resident and South Korean citizen that my entrance could have some good effect."

First message to world

Joo was born in Seoul, South Korea and moved to Wisconsin with his family in 2001. He says he later moved to Rhode Island.

He says he has not spoken to his parents or any representatives of the United States or South Korean governments.

His interview with CNN is his first opportunity to send any kind of message to outside world.

"Of course I understand my parents and my loved ones are worrying a lot about me. But I would like to say that I'm well and there's no need to worry because the people here have treated me with the best of humanitarian treatment," he says.

Joo says he's healthy and well fed. His room has three beds and a private bathroom. He has no access to television, radio, or the Internet. He has not been able to make phone calls.

"I understand that I cannot make outside contact because I did enter the country illegally," he says. "I did commit a wrong act so I understand that I cannot freely move around because I'm currently a criminal."

Joo says he has not been informed if he'll face charges or when he will allowed contact with his family or the outside world.

Arrested in April

North Korean state media reported Joo's arrest on Saturday, more than one week after his arrest on April 22.

The North Korean Central News Agency said the student had illegally crossed into North Korea from China, via the Yalu River, and had "admitted that his illegal entry was a serious violation" of North Korean law.

In a regular press briefing on Monday, South Korea's Unification Ministry spokesman said it was "extremely regrettable" that North Korea had detained Joo without notifying his family or South Korean authorities.

"Our government strongly urges North Korea to repatriate student Joo to his family as soon as possible," said spokesman Lim Byeong-cheol.

On Sunday, CNN interviewed two other South Koreans being held by North Korea, who has accused them of being "spies."

In separate interviews, with North Korean minders present, the two South Korean men -- Kim Kuk-gi and Choe Chun-gil -- said they admitted the allegations against them.

South Korea has also called for their release. In March, the South Korean National Intelligence Service denied the men had been working for the agency.