These days, the eeriest thing about the demilitarized zone in Korea, the world’s most fortified border, is the silence. From a South Korean mountaintop, you can peer through a powerful telescope across the no man’s land of the D.M.Z., past the wide Imjin River, and into the rising hills of North Korea. On the other side, an enormous statue of the country’s late founding father, Kim Il Sung, is posed confidently astride a pedestal, facing south, as if he were heading in that direction.

For years, both Koreas waged psychological war along this hundred-and-sixty-mile frontier. From the South, banks of huge loudspeakers—some stationary and some mobile—blared news from the outside world, messages urging North Koreans to defect, and annoying K-pop music. They were so loud that they could be heard six to twelve miles away. In 2015, North Korea threatened to attack the sound system for its critical and high-decibel-blasting broadcasts about the country’s leader, Kim Jong Un. Pyongyang countered with its own propaganda, albeit less audibly, because of electricity shortages.

This month, the loudspeakers on both sides were dismantled. It was the first step taken after the summit of Korean leaders, on April 27th, and ahead of President Trump’s meeting with Kim, on June 12th. The only sound in the D.M.Z.—for now, anyway—is a howling wind.

The new diplomacy is still fragile. In a surprise announcement, North Korea indefinitely suspended the second round of talks between senior officials from the two Koreas—due to be held at the D.M.Z. on Wednesday. It blamed joint military exercises between South Korean and U.S. military forces. Pyongyang viewed the operation as “a flagrant challenge to the Panmunjom Declaration and an intentional military provocation running counter to the positive political development on the Korean Peninsula,” North Korea’s state-run Central News Agency reported.

The Trump Administration was totally blindsided by the move, just five days after Secretary of State Mike Pompeo returned from his second round of talks with Kim to prepare for the Trump summit. Kim had even told Pompeo that he understood the “need and utility” of continued exercises between two countries with which North Korea is still technically at war, the State Department told reporters. The White House scrambled to clarify and respond.

“We are aware of the South Korean media report. The United States will look at what North Korea has said independently, and continue to coordinate closely with our allies,” the White House press secretary, Sarah Huckabee Sanders, said in a statement.

It was a bizarre turn in what has been highly unusual diplomacy since North Korea initiated outreach, on January 1st. Over the weekend, North Korea had just promised to take the next step forward in a ceremony over three days, from May 23th to May 25th, to dismantle its Punggye-ri nuclear facility. It pledged to plant explosives in tunnels deep under Mt. Mantap, where six nuclear tests have been conducted since 2006, and blow it up. A pool of foreign media correspondents, the North claimed, would be invited as witnesses. “A very smart and gracious gesture!” Trump had responded in a tweet, on Saturday.

Kim, the third leader from a dynasty that has ruled North Korea for seven decades, is a master gamesman. If he ever follows through, destroying the nuclear-test facility would make for high theatre—and recurrent cable-news cycles—but perhaps won’t be much of a concession. The sixth nuclear test, in September, was estimated to be eight to seventeen times stronger than the bomb dropped by the United States on Hiroshima, in 1945. But the North Korean test also triggered an artificial earthquake that registered a magnitude of 6.3, according to the U.S. Geological Survey. It shook houses far across the border, in northeastern China. U.S. and Chinese scientists subsequently claimed that Mt. Mantap—suffering from “tired mountain syndrome”—was sufficiently unstable and that the tunnels might now be unusable. (Both the United States and the Soviet Union also suffered earthquakes after carrying out nuclear tests.) A recent report in Science magazine suggested that the mountain may now be slowly collapsing.

North Korea has long depended on tunnel technology. Tunnels hide some of the country’s biggest secrets. Between 1974 and 1990, four tunnels were discovered running from the North under the D.M.Z. deep into South Korea. There may be dozens more still undetected, South Korean officials told me. Pyongyang dug the tunnels through bedrock and later equipped them with lights and ventilation, to infiltrate troops into the South in the event of war. I visited the so-called Third Tunnel of Aggression earlier this month. It came within thirty miles of Seoul. It was large enough for thirty thousand troops to pass through in an hour. It was detected, on a tip from a North Korean defector, in 1978.

Visitors can now tour the tunnel after clearing a South Korean military checkpoint into the D.M.Z. You put on a hard hat and take a little tram down a steep slope, two hundred and forty feet into the earth. A list of instructions advises, in English and Korean, “Do not enter the tunnel drunk” and “People with respiratory and heart problems should not participate in this tour.” Claustrophobia, too. Access to the tunnel ends at a concrete slab installed by the South to demarcate the border.

Outside the tunnel, I took pictures—in a sign of the tentatively changing times—of fourteen South Korean soldiers posing in playful positions around three giant initials: a red “D,” a dark-green “M,” and a bright-blue “Z.” South Koreans of disparate political positions are generally relieved at the prospects of imminent American diplomacy—after the escalating “fire and fury” rhetoric by Trump last year—and a hiatus from the noise tensions.

There’s a near-desperate hope in South Korea that Trump’s top-down diplomacy—embraced impulsively by the President—will fare better than the deliberate step-by-step negotiations tried by the Bill Clinton and George W. Bush Administrations, which failed. Trump has been offering the biggest reward up front. By agreeing to a summit, in Singapore, he was basically offering legitimacy to a ruthless Communist regime and, potentially, providing the aid that would allow it to survive.

“We can create conditions for real economic prosperity for the North Korean people that will rival that of the South, and that is our expectation,” Pompeo told CBS’s “Face the Nation,” on May 13th, three days after returning from his second trip in two months to Pyongyang. “It will be American know-how, knowledge, entrepreneurs, and risk-takers working alongside the North Korean people to create a robust economy.”

The challenge will be what North Korea actually surrenders. Kim will have to confess the location and details of hundreds, maybe even thousands, of tunnels on the other side of the D.M.Z. which hide his military treasures. “Some think North Korea has built ten thousand underground facilities since the nineteen-sixties,” the retired lieutenant-general In-Bum Chun, a former director of operational planning for the South Korean Joint Chiefs of Staff, told me. The facilities reportedly include troop bunkers along the D.M.Z.; facilities for up to five thousand metric tons of chemical weapons, one of the world’s largest stockpiles; underground hangars; and three underground runways to allow tunnel takeoffs by military aircraft.