From the outside, the train that has prompted speculation of a surprise visit to China by North Korea leader Kim Jong Un doesn't look all that exciting.
It's painfully slow-moving, and drab green with yellow piping that runs along the side.
But inside — if the distinctive train that pulled into Beijing on Tuesday is indeed the same one used by Kim's father, as many believe it to be — there's a lot of bling aboard.
"It had a reputation for being an opulent ride for the leader. It maintains the North Korea leader's lifestyle wherever he goes," said Curtis Melvin, a researcher at the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies. "It is capable of carrying the type of food and entertainment to support the leader as he travels."
For Kim's father and predecessor, Kim Jong Il, that meant live lobsters, wine shipped in from Paris, and four young female singers who were reportedly referred to as the "lady conductors."
State media has not confirmed that Kim Jong Un was the mystery guest aboard the train that arrived in Beijing, although Bloomberg News, citing three unnamed sources with knowledge of the visit, reported that it was him. There was also speculation that it might be Kim's sister, Kim Yo Jong, who recently showed off her high profile at the PyeongChang Olympics.
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Key moments in 2017 between US and North Korea
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Key moments in 2017 between US and North Korea
NEW YEARS DAY MISSILE LAUNCH
On January 1, 2017, North Korea's leader Kim Jong Un warned that an intercontinental ballistic missile (ICBM) was in the 'final stages' of development.
On February 12, North Korea tested a ballistic missile, but it didn't appear to be an ICBM due to its flight range.
NUCLEAR CRISIS AT MAR-A-LAGO
President Trump was at his Florida resort Mar-a-Lago having dinner with Japanese Prime Minster Shinzo Abe when news broke that North Korea had launched a ballistic missile on February 12.
The president sparked controversy by reportedly discussing the event in front of Mar-a-Lago diners while continuing his meal with the Japanese leader and other guests.
Secretary of State Rex Tillerson said military action against Pyongyang was 'on the table' and Trump tweeted that the nation is 'behaving very badly.'
COVERT PHOTO OF TILLERSON
During a visit to North Korea's border on March 17, Secretary of State Rex Tillerson was unwittingly photographed by a North Korean soldier, who can be seen peering into the room on the right side of the image.
The U.S. military warned it was 'prepared to launch a preemptive strike' against North Korea if there were signs the country was planning to test a nuclear weapon.
POLL SHOWS US CONCERNS
A poll conducted by CBS News in April showed that more than half of Americans said they were 'uneasy' about President Trump's ability to deal with North Korea.
FAILED MISSILE TEST
North Korea celebrated the 105th anniversary of Kim Il Sung's birth, North Korea's founder, by unveiling powerful new missiles in April.
The next day, a North Korean missile 'blew up' just a few hours before Vice President Mike Pence arrived in South Korea for a diplomatic trip.
President Trump called North Korean dictator Kim Jong Un 'a pretty smart cookie' in an interview that went viral on April 30.
'At a very young age, he was able to assume power. A lot of people, I'm sure, tried to take that power away, whether it was his uncle or anybody else. And he was able to do it. So obviously, he's a pretty smart cookie,' Trump told CBS News.
The president also said he'd be 'honored' to meet with the North Korean leader.
KIM JONG UN'S LETTER TO CONGRESS
In early May, North Korea said it would continue its nuclear weapons tests and boost force 'to the maximum' in a stark warning to the U.S.
Pyongyang also condemned President Trump for directing the peninsula to the 'brink of nuclear war.'
Soon after, North Korea sent a rare letter to the U.S. House of Representatives to protest tougher sanctions on the nation.
TRUMP GETS HEAT AT HOME
In Washington, Trump was met with criticism from several lawmakers over his handling of North Korea.
Former Secretary of State Condoleezza Rice sounded off on the issue, saying Trump 'can't meet with Kim Jong Un' as he'd discussed.
In late May, a transcript of a phone call between President Trump and Philippine President Rodrigo Duterte was leaked to the public.
The transcript showed President Trump call North Korea's leader a 'madman with nuclear weapons' who could not be let on the loose.
'BIGGER GIFT PACKAGE' FOR US
As tensions continued to ramp up in May, North Korea launched another ballistic missile test and warned the U.S. of a 'bigger gift package' in the future.
'I'm just trying to open the door,' he told reporters. 'My purpose is to actually to see if I can keep bringing sports to North Korea, so that's the main thing.'
OTTO WARMBIER
Otto Warmbier, a 22-year-old University of Virginia student from suburban Cincinnati, was released from North Korean custody on June 13.
Warmbier had been imprisoned in North Korea since early 2016 after he was accused of trying to steal a propaganda sign from a hotel while visiting the country as a tourist.
North Korean officials said he got botulism and was given a sleeping pill, but never woke up.
Warmbier's father said his son suffered a serious neurological injury was 'brutalized.'
Otto Warmbier died on June 19 from lack of oxygen and blood to the brain, according to a U.S. coroner.
TRADING INSULTS
President Trump tweeted in June that diplomacy 'has not worked out' with North Korea, suggesting a potential change in policy.
Pyongyang called Trump a 'psychopath' two days later.
SUCCESSFUL LAUNCH OF ICBM
On July 4, North Korea successfully test-launched an ICBM for the first time ever. The missile flew a trajectory that could hit Alaska.
President Trump responded via Twitter: 'North Korea has just launched another missile. Does this guy have anything better to do with his life?...'
The president later vowed to 'confront very strongly' the issue of North Korea's 'very, very bad behavior.'
U.N. Ambassador Nikki Haley said North Korea's actions were 'quickly closing off the possibility of a diplomatic solution' and that the United States was prepared to use force 'if we must.'
'PILE OF ASH'
In a bold statement, North Korea threatened to turn the U.S. into a 'pile of ash' on July 12.
US THREATENED WITH 'MERCILESS BLOW'
On July 27, a North Korean spokesperson said, 'Should the U.S. dare to show even the slightest sign of attempt to remove our supreme leadership, we will strike a merciless blow at the heart of the U.S. with our powerful nuclear hammer, honed and hardened over time.'
A CNN poll in August showed that most Americans saw North Korea as a 'very serious threat' at that point.
US TOLD TO 'ACT PROPERLY'
President Trump said the U.S. military was 'locked and loaded' in a series of new threats against Pyongyang.
North Korea responded by saying, 'If the Trump administration does not want the American empire to meet its tragic doom..., they had better talk and act properly.'
MISSILE FLIES NEAR JAPAN
On August 29, North Korea fired a missile over Japan that landed in waters near the country, marking a major escalation of tensions on the Korean peninsula.
After Pyongyang conducted its biggest missile test to date on August 29, one of its top diplomats said it was ready to send 'more gift packages' to the United States.
North Korea later threatened to 'sink' Japan and reduce the United States to 'ashes and darkness.'
President Trump called North Korean leader Kim Jong Un 'rocket man' twice, first during an address before the U.N. General Assembly in September and again on Twitter:
'I spoke with President Moon of South Korea last night. Asked him how Rocket Man is doing. Long gas lines forming in North Korea. Too bad!'
Trump claimed the nickname was meant to be a compliment.
'DOTARD'
Kim Jong Un called President Trump 'mentally deranged' and said he would 'totally destroy' the U.S. after he was dubbed 'rocket man' in a U.N. speech.
The North Korean leader also slammed President Trump as 'a frightened dog,' a 'dotard' and 'gangster fond of playing with fire' in a statement released on September 22.
TRUMP VISITS ASIA
President Trump brought up North Korea during a trip to Japan in November, saying 'no dictator' should underestimate the U.S.
Trump's planned visit to the DMZ was canceled due to weather.
'Why would Kim Jong-un insult me by calling me "old," when I would NEVER call him "short and fat?" Oh well, I try so hard to be his friend - and maybe someday that will happen!'
NOVEMBER MISSILE LAUNCH
North Korea fired what is believed to be an ICBM on November 28 that landed near Japan.
Trump responded by saying, 'It is a situation that we will handle.'
A North Korean official said the U.S. was 'begging for nuclear war' and participating in an 'extremely dangerous nuclear gamble.'
On December 20, it was reported that North Korea is testing whether its ICBM weapons are capable of carrying anthrax.
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It's also not clear what the interior of the train might look like these days. Past glimpses of it, however, during Kim Jong Il's regime revealed it to be a party train on the inside and a massively secure form of transportation on the outside.
The train has tinted windows, and according to a 2009 South Korea news report based off of classified information about how Kim Jong Il traveled, is heavily armored. It's also accompanied by many security personnel.
"To defend Kim against attack, two separate trains precede and follow the main entourage, one handling reconnaissance and the other security," South Korean newspaper Chosun Ilbo said of Kim Jong Il's travels. "The advance train handles security checks to see whether the rail tracks are safe. Behind Kim's train is another carrying his bodyguards and other support personnel."
Kim Jong Il's train consisted of 90 carriages, Chosun Ilbo reported, and traveled at an average speed of 60 km per hour — a meager 37.28 miles per hour — while 100 security agents would sweep stations for bombs before the train pulled .
For Kim Jong Il, who was rumored to have a fear of flying — plus a flair for lavishness — It was a comfortable way of travel.
According to Russian official Konstantin Pulikovsky, who accompanied Kim Jong Il and his entourage on a three-week journey to Moscow in 2001 and wrote about the experience in a 2002 memoir, "Orient Express: Through Russia with Kim Jong Il," meals on the train would often last for four hours, and included fresh live lobster or other delicacies.
''It was possible to order any dish of Russian, Chinese, Korean, Japanese and French cuisine,'' Pulikovsky wrote.
For entertainment, there were Russian and Korean songs: Kim Jong Il was particularly fond of four of his female singers who were introduced as "lady conductors," Pulikovsky wrote.
And while the train has long been a source of intrigue, unlike some other aspects of the North Korean regime, it isn't entirely closed off from the public.
Inside North Korea:
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Inside North Korea's Masikryong Ski Resort
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Inside North Korea's Masikryong Ski Resort
This photo taken on February 19, 2017 shows members of a 'ski camp' at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 19, 2017 shows a general view of the lobby of the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
In this photo taken on February 20, 2017, Kim Chol-Nam, 30, poses for a portrait at the ski hire desk where he works at the Masikryong, or Masik Pass, ski resort near Wonsan.
The resort was opened in 2013. A price list at the ticket desk advertises a cost of 80 US dollars for a one-day lift pass and ski hire for foreign tourists, while North Koreans can expect to pay the equivalent of around 40 US dollars. / AFP / Ed JONES (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 19, 2017 shows members of a 'ski camp' at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 19, 2017 shows a room at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 20, 2017 shows staff at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 19, 2017 shows North Korean visitors at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 19, 2017 shows a skier at the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
This photo taken on February 20, 2017 shows a general view of the Masikryong ski resort, near North Korea's east coast port city of Wonsan.
Work began on Masikryong ski resort, the only one in the North and the brainchild of Supreme Leader Kim Jong-Un, after Pyeongchang in the neighbouring South was awarded the 2018 winter Olympics. / AFP PHOTO / Ed JONES / TO GO WITH NKorea-tourism-leisure-ski-diplomacy,FEATURE by Sebastien Berger (Photo credit should read ED JONES/AFP/Getty Images)
In this photo taken on February 19, 2017, Pak Han-Song, 11, poses for a portrait on a beginner's slope at the Masikryong, or Masik Pass, ski resort near Wonsan.
AFP was told that Pak was a member of a youth ski camp. The Masik resort was opened in 2013. A price list at the ticket desk advertises a cost of 80 USD for a one-day lift pass and ski hire for foreign tourists, while North Koreans can expect to pay the equivalent of around 40 USD. / AFP / Ed JONES (Photo credit should read ED JONES/AFP/Getty Images)
WONSAN, NORTH KOREA - JANUARY 29: An Italian-made Areco snow cannon sits on the beginner slope in front of the Masikryong Hotel at the new Masik Ski Resort January 29, 2014 near Wonsan in northeastern North Korea. The screen displays music videos of popular North Korean songs, as well as statistics about mountain conditions. The resort reportedly boasts a 250-room, eight-story hotel for foreigners, 10 ski runs and is thought to have cost $300 million. (Photo by Jean H. Lee/Getty Images)
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At Kim Jong Il's mausoleum in the North Korean capital of Pyongyang, the office car that he once used is preserved at a museum exhibit, complete with a desk and computer — proof, guides at the mausoleum say, according to the Associated Press, that the leaders never stopped working for their people.
Kim Jong Il also allowed cameras onto the train multiple times during his reign, which revealed flatscreen TVs mounted on the walls, laptop computers, conference rooms and satellite phones, which allowed him to be briefed on security issues.
It's not unusual for North Korea to send a leader overseas without any advance notice. In 2003, for example, Kim Jong Il made a trip to China, but it wasn't announced until days later, the AP said.
For Kim Jong Un, such a surprise visit would mark his first known trip outside North Korea since he took power in 2011 — and a sign that he's making overtures to hold diplomatic talks ahead of a planned meeting between himself and President Donald Trump by May.
"This would be yet another sign that Kim is trying to push forward a diplomatic track that we have not seen from North Korea ever before," Victor Cha, senior adviser and Korea chair for the Center for Strategic and International Studies and an NBC News contributor, told the "Today" Show.
As for why he might choose to travel by train like his father — and grandfather — used to do, the experts don't know. Melvin, the Korea researcher, said Kim Jong Un has been building runways throughout the nation is likely usually traveling by air.
But Melvin speculated it might have been over security concerns that something could happen if Kim Jong Un were to fly.
"There is something to be said about security in North Korea right now. If Kim Jong Un were to become incapacitated or die in an accident, this would cause a tremendous amount of confusion and instability in North Korea," he said. "It's a unipolar political system, and a lot of the people in power are basically in power at the behest of Kim Jong Un. There's no mitigating institutions that power has been decentralized to maintain stability in that event."