Billund, Denmark - Millions of people around the world instantly recognize the look, the feel — especially under foot — and even the sound of LEGO. The plastic blocks have shaped childhood memories for generations. 

At the company's home in Denmark, decades of those experiences are captured inside a secret museum that only LEGO employees can access. CBS News, however, got a rare look inside that little-known museum, where it was possible to trace the evolution of one of the world's most recognizable and beloved toys.

The museum sits next to the original home of LEGO's founder, Ole Kirk Kristiansen — a reminder of the toy giant's humble beginnings. The brand's name reflects its philosophy: "LEGO" comes from the Danish phrase "leg godt," or "play well." 

Inside the museum are some of the very first LEGO bricks, including pieces that date back to the 1950s. Among the earliest creations housed there is the first LEGO "system" that was ever assembled — a small town that laid the foundation for everything the company would go on to build. 

That system — the idea that every LEGO brick, regardless of when it was made, can connect — dates back to 1955, when the company assembled that first play town. Over the decades, LEGO creations have evolved from medieval villages to mind-blowing architectural feats.

The collection features vintage sets that continue functioning as they were designed to, many decades later, including a working drawbridge castle from the 1970s. But there's been no shortage of evolution, either. From the early designs, LEGO's builds have grown increasingly ambitious and sophisticated. 

Along with the classics, the museum showcases intricate creations ranging from miniatures of iconic landmarks such as the Eiffel Tower to LEGO flower bouquets. Other pieces have evolved from LEGO's own sub-brands. Many of today's parents will be familiar, for instance, with armies of tiny characters from the modern kids' TV fantasy superhero show Ninjago.

Inside Lego House 

CBS News also got a glimpse inside LEGO House, a nearly 130,000-square-foot monument to the toy, filled with some 25 million LEGO bricks, including those of the 6 million-plus that make up the striking "Tree of Creativity."

Standing nearly 50 feet high, it's the largest known LEGO build in the world. Each branch is packed with detail, a feast for the eyes. 

Behind all the creations is LEGO's own in-house army of creatives. 

"There are about 700 designers here," André Doxey, the LEGO Group's first American Head of Design, told CBS News. 

Doxey said creativity, not technical skill, has been key to LEGO's enduring appeal. 

"You don't have to be a designer," he said. "You just have to be brave, creative and curious, and give it a try." 

Doxey believes LEGO's remarkable enduring popularity is owed largely to the freedom it offers. 

"We know people love to create, kids love to create," he said. "Our system is a creative medium. It enables them to imagine anything they want to imagine."

LEGO: Not just for the kids — but mainly for the kids

And LEGO has found that the appeal extends well beyond childhood. Nostalgia plays a powerful role at the company, and so-called AFOLs — Adult Fans of LEGO — represent a significant and growing market.

But Design Master Milan Madge knows the audience well, and while not denying the rising popularity of more complex, grown-up builds, he said children remain the company's priority. 

"They're our first inspiration," he said. "We try to act like children and see the world through their eyes."

While modern designs are often created digitally to streamline production, Madge said he still prefers working with physical bricks. 

"There's a real connection between the mind and the creative process when you're doing hands-on work," he said.

That simple tactile connection — brick by brick — has helped make LEGO the top-grossing toy company in the world. Families build together. Friends gather around shared creations. Communities form, united by the sound of bricks rattling in a box. 

"Everyone knows that sound," Doxey told CBS News. "You shake it, and you know exactly what it is."

A beloved toy, with a plastic problem

Beyond all the creativity and the nostalgia, however, the LEGO Group is also grappling with a fundamental issue in a world facing what a majority of scientists say is a climate crisis: The company's empire is still built almost entirely on plastic, and one of the key components in most plastic is fossil fuel.

Every ton of LEGO produced requires about two tons of petrochemicals in the manufacturing process, according to the global sustainability information and data platform, illuminem. LEGO makes approximately 60 billion bricks per year, and based on illuminem's data, some of the company's largest sets would require the equivalent of over 60 pounds of petrochemical equivalent to produce. 

Despite ambitious climate pledges, the company has so far failed to find a sustainable path for its toys. 

LEGO abandoned a "bottles to bricks" initiative in 2023 after finding the proposed recyclable material it hoped to use would, in fact, increase emissions compared to its current materials.

"LEGO bricks are made for children, so they must meet extremely high quality and safety standards," the company told CBS News in a statement. "They must also be durable, and are precision-engineered to accuracy of less than a hair's width so that a brick made today still fits one made 60 years ago."

The company said it has tested more than 600 different materials for its LEGO bricks, including some derived from "sustainable-sourced sugarcane" and recycled materials from artificial marble kitchen countertops.

"Other materials have shown potential, but have not met our strict quality, safety and durability requirements, or would not have helped reduce our carbon footprint," the statement said, adding that the company is on track for "60% of the materials we buy to be produced from sustainable sources" by the end of the year.

Even after all these years, LEGO continues to evolve.