After the two leaders pledged new steps aimed at salvaging nuclear talks on Wednesday, Moon and Kim made a decision to use the final day of their three-day summit to go up the symbolic mountain on the Chinese border together.
North Korea's pledge at a summit with South Korean President Moon Jae-in in Pyongyang drew an enthusiastic response from Mr Trump, even though some USA officials and experts fear a ploy to weaken Washington's resolve and its alliance with Seoul.
"There is our old saying that we greet the sun at Paektu, and greet the unification at Halla", Kim's wife, Ri Sol Ju, said.
"South and North Korea agreed on a denuclearisation plan for the first time". He said, "The era of no war has started".
In a pair of late-night tweets, Trump described Kim's moves to discuss allowing nuclear inspectors, in addition to dismantling a missile test site and putting in a joint bid to host the 2032 Summer Olympics with South Korea, as "Very exciting!".
North Korea says Kim's grandfather and father were born at Mount Paektu, a centrepiece of the North's idolization and propaganda campaign to highlight the ruling family's sacred bloodline.
USA intelligence services allege that North Korea is still enriching uranium and hawks on North Korea are disappointed about the latest meeting.
"But it is no closer to North Korean disarmament", he said.
In a statement to the press after the meeting, Kim told reporters that he and Moon had "made a firm commitment to exert active efforts to make the Korean Peninsula free of nuclear weapons and nuclear threat and turn it into a land of peace". "The road to our future will not always be smooth, and we may face challenges and trials we can't anticipate, but we aren't afraid of headwinds because our strength will grow as we overcome each trial based on the strength of our nation".
With the main business of the day over, North Korea was expected to hold a huge mass games spectacle in the evening, with Moon as the special guest. "We have lived together for 5,000 years and lived in separation for 70 years. I use this opportunity to propose taking a big step toward peace and to end 70 years of hostility".
Moon's visit to the mountain was the realization of a dream for the South Korean leader. They agreed as well to restart a joint factory park in a border city of Kaesong and tours to the North's Mount Kumgang resort, when conditions are met.
The two sides agreed to break the impasse during Kim Jong Un's historic meeting with Trump in Singapore in June.
It represents glorious achievements like North Korea's nuclear weapons development and extols the regime of the Kim dynasty, though Wednesday's performance cut about 30 minutes of the most blatant propaganda. They also agreed to withdraw 11 guard posts from the Demilitarized Zone by December and to establish a no-fly zone above the military demarcation line that bisects the two Koreas that will apply to planes, helicopters and drones. And they either pocket the concession and then move on to the next demand.