Seoul (CNN) — Even in a country where nearly everyone is connected to ultra high-speed internet, the spectacle of fireworks exploding from one of the world's tallest buildings can still pull in the crowds.

But perhaps even more impressive than the display that entertained onlookers at the 123-story Lotte World Tower in Seoul earlier this month was the daredevil effort that went into creating it.

The 11-minute show required a $6 million budget, 30,000 fireworks and 750 shooting spots, but also some terrifying ropework, half a kilometer above the ground, by highly experienced mountaineers.

This is where Group F came in. A 37-strong team of mountain guides, rescue workers and rigging experts from France, they specialize in setting up fireworks on landmark high-rise buildings around the world such as the Eiffel Tower or Dubai's Burj Khalifa.

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In Seoul, their operations began several days before the show, with the arrival of a truck carrying gunpowder racks. The team used elevators then staircases to take the gear up to two spots where they could gain access to the building's exterior -- on the roof and the 73rd floor.

Group F's experts think nothing of clinging to the side of a skyscraper. CNN

This is the part when most people's legs would start to wobble as they cling on for dear life, but for Group F's Eric Faroux, letting go and swinging out high above the streets is just another day at the office.

"When it has been your job for 20 or 25 years, it's something you don't think about it in the end," he says. "You don't have fear. You need to concentrate. When you cross the fence, you don't have fear."

Faroux and his colleagues liken a building to a mountain and refer to the top as the summit.

But, given the fact they're handling potentially dangerous explosives, it's arguably tougher terrain.

Lethal drop

"Ooooh, ahhhh!" $6 million goes up in smoke. CNN

Even an object as small as a pen could have proven lethal to pedestrians below if dropped.

As a precaution, the area around the base of the building was closed off during the operations.

"Safety is the major consideration in this project so the team has been chosen [with that consideration in mind]," says Fauroux.

Group F's experts, equipped with safety gear including a helmet, harness and rope, work in pairs or teams of three when they're rigging. In the case of Lotte, they each descended on a single rope to one of the 370 firework launch spots.

When the time came to light the fuse, crowds gathered at several locations on the ground, nearby rooftops or in parks -- the display was a highlight of this year's traditional family month celebrations.

There was a theme of peace this year -- a reflection of the recent rapprochement efforts with North Korea. There was also music from "La La Land," "The Greatest Showman," and a famous Korean traditional song, "Ariang."

The show climaxed with loud bangs and blinding flashes, revealing the Korean word for "peace."