It was a visit to Pyongyang's Yanggakdo Hotel that resulted in the detention and eventual death of American student Otto Warmbier. US doctor Calvin Sun recalls his night inside a secret floor in the hotel and warns other travellers to stay away.
Calvin Sun had been awake for almost 24 hours when North Korean guards boarded the minibus that was due to take him and his friends to Pyongyang International Airport and out of the country.
There was an issue, the officials announced. The group would not be allowed to leave until it was resolved.
The bus fell silent.
Sun thought back to his one-week excursion to the most isolated country in the world, nicknamed the Hermit Kingdom. It had been one of his most memorable trips.
"Of all the things we had done in North Korea that week," says Sun, "it never occurred to me that our visit to the fifth floor may have been the problem."
It still didn't cross his mind when the guards asked the travel group to step out of the minibus.
Calvin Sun was born and raised in New York City by Chinese parents. By the time he reached his 20s, he had barely left the state. As an undergraduate at Columbia University, 20 minutes away from his home in New York, he didn't like venturing outside his comfort zone.
But a spontaneous trip to Egypt in 2010 sparked a thirst for exploring the world. He set up a travel blog, The Monsoon Diaries, and quickly gained a cult following.
Sun used every break and weekend to explore a new country, with the goal of never repeating an experience or going back to the same place.
Before his second year at medical school, Sun decided to use the summer break to embark on a trip that would start somewhere in the Middle East and end somewhere in Asia. He kept his itinerary fluid, allowing for spontaneous excursions with friends he would make along the way.
North Korea was not part of the initial plan. Neither was the secretive fifth floor of Pyongyang's Yanggakdo Hotel.
Western tourists wanting to visit North Korea in 2011 needed the assistance of a private tour operator. Around half a dozen international travel agents offered bespoke guided tours for groups to North Korea through China. The rules for these visits were tightened in 2017 - in part, many believe, due to one fateful trip made by a Western student to the forbidden fifth floor of the Yanggakdo Hotel.
While in Beijing, Calvin Sun had a week to spare before his return to the US. He visited one of these tour operators to browse through their itineraries. The secretive state of North Korea seemed too enticing an opportunity to pass up. He opted for the tour that gave him the best deal.
"North Korea was one of the easiest visa forms I had to fill out. You didn't even need to hand in your passport to apply for entry then. I think many people don't even bother to try because the thought of it is too overwhelming."
This would be the final country Sun would visit before returning home to New York and his second year of medical school.
Sun, along with a group of 20 American, European and Chinese travellers, mostly in their 20s, met their tour organisers in Beijing. During an orientation session, the group were told to listen to their guides and to always show respect for North Korean culture.
They would be staying at the Yanggakdo Hotel in the capital. The fifth floor, however, was never mentioned.
Landing at Pyongyang International Airport, Sun was immediately struck by the contrast with China.
"It was as if God had muted the colour," he says, "Beijing had been so colourful that it now seemed garish next to Pyongyang."
"The buildings, the posters, the signs, the clothes were white, grey and black with maybe a little bit of red. Communist party colours. It was as if I'd got into a time machine and arrived inside a 1970s Soviet TV show time warp."
Three guides in their 40s, two male and one female, were in charge of running the packed tour. They informed the group that they used to be officials in the DPRK military.
"Although they seemed a little strict and organised in the beginning, telling us not to cross streets without supervision or take photos of certain buildings, we formed an instant rapport with them," says Sun. "The guides enjoyed drinking. We learned that alcohol is a central part of Korean culture, and they encouraged us to socialise with them every evening."
The trip saw the group visit landmarks like Juche Tower, the Worker's Memorial, the USS Pueblo - the only US Navy ship still on the commissioned roster to be taken hostage by North Korea in 1968 - and the Demilitarised Zone. But it was the moments drinking and socialising where Sun saw true glimpses of how the country - which has state-controlled internet and limited TV access to mostly propaganda broadcasts - views the US.
"The guides were fascinated with Michael Jackson and kept asking us if he died of Aids. They also asked us a lot about police brutality in America. The American reality show Cops, which follows police officers on real-life stings is one of the few international shows that was shown on North Korean TV (at least to the officials). They asked a lot of questions about that."
But it wasn't just the content of the questions that struck Sun. It was the way they were asked.
"It seemed more than curiosity, as if they were trying to get confirmation of a very particular view they had of the US."
Sun shot a gun for the first time at a North Korean shooting range in the countryside. Most of the group missed the target. Their ineptitude caused the guides to wonder out loud in surprise at how Americans, with their experience of gun violence, could be so bad at shooting.
As the week progressed, the stringent rules drummed into them at the start had relaxed. The guides were no longer bothered if the group crossed roads unsupervised. They were no longer briefed to not take photos.
It had been a memorable week. Sun had made fast friends with his travel companions and felt at ease with the guides. On their last night together the group went to a nightclub called Diplo and danced to music from the 80s, predominantly Michael Jackson.
Back at Yanggakdo Hotel, the guides encouraged the group to once again join them for drinks. They didn't stay long. It had been a busy week.
The group started to make their way to their respective bedrooms, when some decided it would be fun to congregate briefly in one room before bed. They weren't as tired as they thought.
It was then that someone suggested they explore the rest of the hotel.
At 47 storeys, the Yanggakdo International Hotel is one of North Korea's tallest buildings. It's located on an island in the middle of the Taedong river, and boasts four restaurants, a bowling alley and massage parlours. TVs in bedrooms play dated BBC World News reports on a loop.
It's by far the most popular place to stay for tourists in the country. The North Korean Tourist board bills it as a five-star hotel, although tourist reviews on travel sites say the standard is closer to three.
"It's almost like they sent someone to Vegas in 1984 and said, 'Look what they've got, come back here and build it.' And they did, but got it all a bit wrong," wrote one blogger.
For their five-night stay at the hotel, Sun and the group had been supervised by their guides. Now was their last opportunity to explore the building alone. After all, there had been no rules against exploring the hotel.
The group made their way to the open rooftop and then to the revolving restaurant on the top floor, before making their way down in the lift.
Someone then noticed that the button for the fifth floor was missing. The numbers on the panel jumped from four to six.
"We should check out the fifth floor, see if they skip it because they're superstitious or if it really exists," another said.
The mystery of what the secretive fifth floor may hold had already been a source of much intrigue among travel bloggers. Some in Sun's tour group, most of them seasoned travellers, had heard of it. Sun had not.
"We weren't the first group to go to the fifth floor - or the last. In 2011 no tourists had ever been detained in DPRK. The weight of what we were doing didn't occur to us."
Today there is a page on Young Pioneer Tours (Sun's tour operators) website stating that the floor is strictly off-limits for tourists. There was no such online warning in 2011. Neither was there one offline.
"We were not briefed to stay away from the fifth floor at any stage by the guides, it just wasn't mentioned," says Sun.
They had also been informed by another traveller who had already been there, that as the fifth floor doesn't technically exist, they couldn't get in trouble for being there.
The group disembarked on the fourth floor and made their way to the stairwell round the back of the hotel. While the mood was outwardly jovial, Sun says they were on edge.
"One of the guys who was walking ahead in the corridor ran back and said 'No not this way, I heard screaming.'" Sun adds that he didn't hear the screaming, but was unnerved enough to pay attention. "We all decided to change direction and head to the sixth floor, and walk down to the fifth floor from there."
The group were surprised to find that the door to enter the fifth floor from the stairwell was unmanned. It was also open. Pulling out their cameras, they stepped inside.
The first thing that struck Sun was the low height of the ceiling. It was around half that of the other floors. Some ducked or tilted their heads to the sides. Keen to explore, the group dispersed.
Sun started walking through the dimly-lit, concrete bunker-like floor. Bar the ceiling height, it looked just like a normal hotel bedroom corridor with doors branching off either side.
Most rooms were locked, but one was open. There was a pair of shoes outside, next to the open door. When they looked, they couldn't see anyone inside.
"This room had lights coming from inside and we saw security cameras, TV screens that seemed to show the inside of bedrooms and what looked like surveillance equipment. I now began to think that this floor was where the hotel staff reportedly kept equipment to surveil guests."
One of Sun's friends on the trip began to film a video as Sun took photos. Everyone was speaking to each other in hushed tones.
"We accidentally used flash photography though - but no one came looking for us."
The walls were covered with brightly coloured anti-American and anti-Japanese propaganda paintings and framed hangings. Several images glorified the former Supreme Leader Kim Jong Il.
One caption read: "This bomb is the product of the Americans. Every product of the Americans is our enemy. Get revenge a thousand hundred times against the Americans."
After several minutes a man they didn't recognise emerged from the shadows and approached the group.
"Lost?" He asked calmly in English.
Someone said yes, they were. The man nodded and pointed them to the stairs.
"He didn't escort us back to our rooms, or appear angry or agitated."
Returning to a bedroom, the group agreed that they did not feel threatened by the encounter with the hotel official. A few decided to venture down again.
Back down on the fifth floor, one of the people in the group opened a door to find nothing but a brick wall. Another opened one to find stairs that led to another floor.
"There was a floor within a floor."
There were more locked rooms and more propaganda posters nailed to the wall. Sun can't read Korean but later, after uploading the video onto YouTube, he found out the meaning of some of the messages. They spoke of revenge on the US and the power of the Kim family. One poster, depicting an early 1980s model computer, heralded the 21st century as the age of technology.
Once again a different hotel official approached the group and once again they were politely asked to return to their rooms.
Some returned for a third time. Even more relaxed this time round, two members of the group wandered off on the floor and kissed in private (this was revealed in a small group reunion years later). Once again, a different guard arrived to good-naturedly point them back to their rooms.
"We were all in our early 20s. We were foolish. We were very naive. The experience seemed exciting and innocent. After everything that has happened since then and taking responsibility, knowing what I know now, I would not have done it."
Sun and the group eventually returned to their respective rooms at 05:00 and packed for their flight out of Pyongyang. Their minibus would be arriving in just two hours time.
At 07:00, the group was still in good spirits as they waited for the minibus to take them to Pyongyang International Airport. But when hotel officials boarded the bus and asked them to disembark, a ripple of concern went through the party.
The guides said they knew of what one member in the group had done and it would be prudent to confess now. The group remained silent.
An official spoke up. Embroidered towels from the private rooms of the Yanggakdo Hotel had been taken without permission. If the group wanted to return to their respective homes, they would need to be returned. No one admitted guilt.
The tour guides made a deal with the officials. If they turned their backs and stepped out of the bus, the offender would place the towels on the floor. It would be the quickest way to resolve the situation, they argued. The guards accepted the deal and the stolen towels were returned without the thief being identified.
The group made their way to the airport and, as is customary, turned in their North Korean visas at the gates and flew out of the country without a stamp on their official passports.
Sun started his second year at medical school the following day. He rarely thought of the fifth floor. That all changed four years later.
In 2015, US university student Otto Warmbier would follow the same programme in North Korea as Calvin Sun, with the same operators, Young Pioneer Tours. Warmbier would also stay at Yanggakdo Hotel. And it was at the hotel that North Korean officials would say that Warmbier attempted to steal a North Korean poster.
Warmbier was subjected to a sham trial and then a forced TV confession. He was convicted and sentenced to 15 years hard labour for the offence. Warmbier sustained injuries while incarcerated and he fell into a coma from which he would not regain consciousness. Otto Warmbier's death in June 2017 made international headlines.
Grainy surveillance footage indicated that Warmbier had been in a part of the hotel not open to the general public. Some who have visited the Pyongyang hotel say that the 21-year-old student had undoubtedly ventured onto the fifth floor and removed a propaganda poster from the wall - a detail never confirmed by the North Korean government or Yanggakdo Hotel, who have similarly never confirmed the existence of the fifth floor.
"While we were there there were no posters that you could take down. The pictures were either all painted or nailed to the wall," says Sun. "Not that we ever had considered taking, let alone touching anything on the floor - there was nothing that we could have stolen from there anyway. Except for maybe the pair of slippers on the floor outside the surveillance room."
Warmbier's death put the spotlight on tourism to North Korea. A number of tour operators, including Young Pioneers Tours, said they would no longer escort US citizens to the country. Many said they would be reviewing their policies for all Western tourists, adding pages on their websites stating that the fifth floor was a service floor that was strictly off limits.
Now an emergency doctor finishing his last month of residency, Sun still continues his travels any opportunity he gets, having gained thousands of followers for his blog. However, he is now more careful about his actions.
"I feel terrible about what happened to Otto. And knowing what we now know, I would certainly advise all travellers to respect the customs of the country they are visiting. But back then, there was no way I could have known that we were being reckless or what we did could have resulted in such a tragic and serious outcome as Otto's."
All photos belong to Calvin Sun and The Monsoon Diaries unless otherwise indicated
Follow Megha Mohan on Twitter @meghamohan
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