Hong Kong (CNN) — Every year for just a few weeks, a towering bamboo theater rises from Ap Lei Chau, one of the world's most densely populated islands.

As many as 1,000 people will pack the 81-feet-wide, 130-feet-long, and 45-feet-high bamboo behemoth in southern Hong Kong, where a Cantonese opera is staged to celebrate the birthday of Hung Shing, the god of the southern sea -- still a revered figure on this former fishing isle.

This is one of about 40 bamboo theaters erected around Hong Kong throughout the year to host performances honoring various Chinese gods.

But their construction is something of a mystery. A bamboo theater has no written blueprint. Workers say they build them based on instinct, rapport and experience -- they learn their trade on the job during apprenticeships.

Today, less than 100 people in Hong Kong specialize in the craft, says Chan Yuk-kwong, owner of Wah Bo Engineering, which executed the Ap Lei Chau project in 2018 -- and has done so each year for the past three decades. But with a lack of young people wanting to join the industry, Chan believes there "will only be fewer companies making bamboo theaters" in the future.

CNN followed the construction of the Ap Lei Chau theater to document this unique architectural feat.

Bamboo city

The men -- and it always is men -- who nimbly scale these vertiginous bamboo grids, often without safety harnesses, are considered by many as much artisans as they are construction workers. Erecting a bamboo theater is perhaps the best example of this craftsmanship.

"It's like doing artwork ... so much of it is unplanned, and I think that's where the beauty of (bamboo construction) lies," says says architect William Lim, who has built around a dozen major bamboo installations, and is founder of Hong Kong-based firm CL3. "It has a lot to do with spontaneous discussion and reaction."

Chan, who is in his 60s, started learning how to build with bamboo at 13 years old. His great-grandfather, who lived in in Guangdong, southern China, specialized in bamboo construction and passed the craft down: most of the men in Chan's family, including his own son, went into the field.

The Ap Lei Chau bamboo theater during the final stages of construction.

Today, Chan's company builds about 30 bamboo theaters per year -- the lion's share of what remains in Hong Kong. In Ap Lei Chau, he led a rotating team of 10 workers over two-and-a-half weeks, and says the weather was the biggest variable. "If it rains, we stop," he explains.

He declined to say how much the Ap Lei Chau theater cost to build.

The foundation

Chan says he has built bamboo theaters in locations as precarious as cliff edges and steep hills, because they have to be located near the temple of the god they will honor. "It's exactly the same as building on flat ground. You just become a lot more careful," Chan explains. "If it's going to be slippery ground then you need to add extra pillars to prevent it from moving."

Luckily, the Ap Lei Chau theater was built on a public soccer pitch, near the Hung Shing temple, which provided a straightforward flat surface.

First off, Chan had to find a way to secure the free-standing theater without building any foundations or using a single nail. To achieve this, his team identified an existing structure at the site onto which a few wooden poles, which are larger and more stable than bamboo, could be attached.

Workers begin building the back of the theater. They are anchoring wooden poles to the soccer goal.

Andrea Lo/CNN

"Traditionally, a bamboo structure has to get its strength from something around it," says Lim. Take, for example, the pockets of bamboo scaffolding protruding from a single apartment when a repair or paint job is needed in the middle of a tall tower. "The strength of the building will allow the bamboo to support itself very nicely against it," says Lim.

The same principle applies when building a bamboo theater. "The (bamboo) structure is anchored to surrounding permanent structures -- so it borrows its strength from the environment," Lim explains. "I think it's a very unusual way of construction, and I've only seen it done in Hong Kong."

In Ap Lei Chau, Chan's team attached two wooden poles in an X-shape to a football goal. From this basic frame, which used the goal for stability, the team then started to build out the bamboo structure in a grid-like pattern tying the rods together using only nylon threads.

Wooden poles lean on existing structures to borrow their strength.

Andrea Lo/CNN

"The whole construction is based on ties and the lightweight bamboo," says Lim.

Taking shape

The team built one entire side of the theater before fleshing out the structure into a box shape. It doesn't matter which wall comes first, Chan says: some workers prefer going from left to right, while others back to front.

Once the bamboo structure had its basic shape -- i.e. there were four walls, and a triangular rooftop mirroring those seen in traditional Chinese architecture -- the wooden poles were removed. The structure was now stable enough to stand without them.

The theater starts to take shape.

Andrea Lo/CNN

When CNN visited on the first day of construction, the site transformed into the skeleton of a theater, with three sides beginning to resemble a box-shaped structure in just a couple of hours. Less than a week later, it had established a solid shape, with the complex inner roofing underway.

Two weeks in, Chan's crew started covering the roof and exterior with metal sheets. Workers prodded a hole in the metal using a spike, then tied a nylon thread through the hole to attach it to one of the rods beneath.

The sheets were overlapped to make the structure rainproof, then bamboo rods placed on top of them as a final touch.

A worker scales the bamboo grid.

Andrea Lo/CNN

The interior is a much simpler affair: around five days before construction wrapped up, Chan built a bamboo stage at the back of the theater. Wood panels measuring 2.5 feet (1 meter) long were then placed atop the bamboo to create flooring.

In final days of construction, wooden supports were added to the exterior of the structure at an angle, to act as a barrier for strong winds. Finally, colorful banners and flags decorated the building.

Inside the bamboo theater.

Andrea Lo/CNN

At the Ap Lei Chau bamboo theater, this year opera performances -- organized by the local neighborhood association -- took place over five days, featuring 13 actors from the Hong Kong-based troupe Ming Chee Sing Chinese Opera. "Cantonese opera is about bringing joy to both the gods and the people," says Chan.

Why bamboo?

To build the theater, Chan's team used 4,000 bamboo rods, 600 wooden poles, and 1,800 metal sheets to cover the exterior. Much of the building was recyclable -- each of of the six- to seven-meter long bamboo rods could be reused in another three projects. Depending on their condition, the metal sheets can potentially be reused three to four times, while the wooden poles can be reused up to 10 times.

"It is a very smart construction system and also very ecological, very environmentally friendly," Lim says.

The banner reads "Celebrating Hung Shing's Birthday."

Andrea Lo/CNN

What's more, "in a congested environment like Hong Kong" bamboo structures are advantageous because they can be constructed and taken down "very easily and very flexibly," he adds.

Indeed, the Ap Lei Chau theater was dissembled in just three days.

Lim believes that heritage buildings in Europe -- such as "parts of a castle that might be 20 or 30 meters off the ground" -- could benefit from the use of bamboo scaffolding. "With a steel or metal scaffolding, you pretty much have to start from the ground and go up. Whereas with bamboo, you can actually just have it come out of the middle of a building ... and become a structure in itself."

Currently, Hong Kong is one of the few developed cities to use bamboo scaffolding. "When people see it, they don't understand how it's done," Chan says. "There's a certain mystery behind it."

Perhaps it's time they found out.