ARI SHAPIRO, HOST:

The White House made it official today. When President Trump travels to South Korea next week, he will not visit the DMZ. That's the Demilitarized Zone which divides the Korean Peninsula. The White House said that was because of time constraints. Despite its name, the DMZ is the world's most heavily armed border. And it's often called the scariest place on earth. NPR's David Welna just returned from this closed military zone and brought this audio postcard.

DAVID WELNA, BYLINE: Just 30 miles from Seoul, a big Chinook U.S. Army helicopter drops me and a dozen other reporters off at a place called Camp Bonifas. It's named after U.S. Army Capt. Arthur Bonifas. He and another American soldier got hacked to death nearby 41 years ago by axe-wielding North Korean border guards. We all get on a bus, where we're greeted by Capt. Akihiro Sanjyo.

CAPTAIN AKIHIRO SANJYO: Together with myself and from Pvt. Goetsch, we'll be your escorts for today.

WELNA: Pvt. Goetsch, our other escort, kicks off the guided tour.

PRIVATE GOETSCH: Looking off to your left-hand side here, past this fence line, you might be able to get a quick glimpse into what we know as the world's most dangerous golf course. It is known for this reason for the fact that it is surrounded on three sides within the joint security area by approximately 2 million land mines.

WELNA: He says the golf course is still used. The land mines, he adds, were planted by all sides in this conflict.

GOETSCH: Now, ladies and gentlemen, the blue overhead sign that we're approaching to the front is the official entry into the southern boundary of the Demilitarized Zone, also known as the DMZ. Ladies and gentlemen, welcome to the DMZ.

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WELNA: We arrive at what's known as Freedom House - looks a lot like a bunker. Defense Secretary Jim Mattis is making his first visit to this part of the DMZ.

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WELNA: Mattis and his South Korean counterpart, Song Young-moo, are let out to a kind of courtyard. It's where an armistice was signed that's put a bloody war on an edgy hold for the last 64 years. The two defense chiefs are received by Col. Steve Lee.

COLONEL STEVE LEE: Gentlemen, welcome to Panmunjom. This is a place of dialogue between United Nations Command and North Korea.

WELNA: Col. Lee points to a dozen green-uniformed soldiers standing just yards away on the other side of a line of concrete that looks like a street curb.

LEE: Directly in front of you is North Korea. So you are being observed, obviously, to the right and to the left by North Korean powers, as well as North Korean soldiers that are right up to the military demarcation line.

WELNA: Mattis is then led into a low, blue building used for talks with North Korea. It straddles that military demarcation line.

Four North Korean soldiers have gone up to the side of the building that Secretary Mattis and the Korean defense minister are inside right now. One of the North Korean soldiers has a pair of binoculars in his hands. He was peering through the windows with them. Mattis comes out and, with his back to the North Koreans, addresses his South Korean counterpart.

JAMES MATTIS: We stand shoulder-shoulder with you, with your soldiers and with your people in confronting the threats posed by the Kim Jong Un regime.

(SOUNDBITE OF MUSIC)

WELNA: Very faint music wafts in from North Korea as Mattis speaks. As we leave, Pvt. Goetsch explains to whom it's directed.

GOETSCH: To the Republic of Korea to defect to their so-called city of paradise.

WELNA: So far, he says, the only defectors are those fleeing to this side of the DMZ. David Welna, NPR News, in the Demilitarized Zone dividing the two Koreas. Transcript provided by NPR, Copyright NPR.