Visitors to Expo 2015 in Milan, Italy, climb on a net suspended over an ersatz rain forest at Brazil’s pavilion. The fair opened May 1 for a six-month run with the theme of “Feeding the Planet. Energy for Life.” (Luca Bruno/Associated Press)

Last month, visitors to Milan’s Expo 2015 — otherwise known as the world’s fair — lined up at Brazil’s pavilion to climb onto a tensile net structure suspended over a vision of a rain forest, complete with sound effects. At the crowded German pavilion, they exited by jumping onto a giant slide. Holland’s featured a Ferris-wheel restaurant, and at the Czech Republic, a large swimming pool outside had a Coachella vibe. The Swiss pavilion was mobbed even on a cold, cloudy Sunday — primarily because costumed “milk maidens” were handing out free apples outside. (Other days, rumor has it, they give away chocolate.)

The American contribution to this 145-country exposition, which opened in May and runs through October, is hardly short on attention-getting, at least when it comes to the design. With a giant American flag (where a plate, knife and fork take the place of stars) and a 7,200-square-foot crop wall (the world’s largest vertical farm), the pavilion rises vast and narrow in steel and glass on the expo’s mile-long main concourse.

But attendees haven’t been lining up around the block to get in. That could be because, at least so far, visitors seem more interested in treating the expo as an amusement park than as a learning experience. And the USA Pavilion is decidedly the latter.

The expo’s theme this year is food, specifically “Feeding the Planet. Energy for Life.” The USA Pavilion — the only one that has been completely privately funded — takes on such global issues as food safety, security and sustainability. For the 20 million people expected to visit the event, the pavilion’s organizers say they have worked to create something that, besides being aesthetically pleasing, offers plenty to think about.

Expo 2015’s USA Pavilion boasts the world’s largest vertical farm: a 7,200-square-foot crop wall along the fair’s main concourse. (Giuseppe Cacace/Agence France-Presse/Getty Images)

As visitors enter the 35,000-square-foot pavilion, they are led up to an expansive walkway featuring reclaimed wood from the Coney Island boardwalk, post-Hurricane Sandy. Here, President Obama issues a video message reiterating the pavilion’s main theme: that each of us is “one in 9 billion” — the United Nations estimate of how many mouths there will be to feed in the world by 2050 — and that the global food system is in our hands.

“We’ve been called the most intellectual pavilion,” said Mitchell Davis, executive vice president of the James Beard Foundation and the pavilion’s chief creative officer.

Indeed, to appreciate the message, you have to pocket your smartphone and start reading — or listening. One afternoon, Marion Nestle, a New York University nutrition professor and one of the nation’s leading authorities on public health, was on the pavilion’s terrace giving a talk on the future of food when a group of high school kids from Rome walked by to take selfies overlooking the expo’s concourse, called the Decumanus. (The expo site is modeled on the layout of a classic ancient Roman settlement, with Decumanus as the main street. The USA Pavilion is one of the expo’s tallest, so the views of Decumanus are prime.)

“I probably would have expected something more from America,” said one of the students, 19-year-old Francesco Vommaro. “This terrace is pretty plain.”

British visitor Emma Winch didn’t like that the roof terrace bar was serving Italian wines. “I think it would’ve been much more interesting to make it 100 percent U.S. products on offer, and maybe showing off some California chardonnay to at least stick to the theme,” she said. But she also acknowledged that she hadn’t had time to stop and look at many of the exhibits over the three levels of the pavilion because she’d been running after her young daughter.

The German pavilion at Expo 2015. (Giuseppe Cacace/Agence France-Presse/Getty Images)

Nonetheless, Winch called the USA Pavilion one of her favorites from a design point of view — at least on the outside. “I think it stood up to the standard European thinking about the U.S., that it likes to grab the limelight a bit in a bigger-is-better kind of way,” said Winch. “Just look at the size of the U.S. flag at the entrance.”

Thankfully for the pavilion’s organizers, some visitors have come looking specifically for something meatier to sink their teeth into.

“My understanding of Expo is that it wishes to create awareness about the challenge of how to feed a growing population with fixed resources,” said Astrid, an American visitor who works in sustainability and who asked that her last name not be published. “Based on my understanding, the USA Pavilion is on the mark. For example, Obama addresses the challenge and creates awareness. The other [interactive] screens touch on the challenge and propose solutions.”

Even those pavilions that offer up a bit more interactive pizzazz, such as the Brazilian net and German slide, still try to stay on message with the expo’s overarching theme. Brazil aims to show how food remains an essential part of social and economic integration in the country, from its history and tradition to the latest technologies. In addition to its slide and “picnic meadow” on the terrace level (complete with beer garden, naturally), the German pavilion includes interactive exhibits with the theme “Fields of Ideas,” meant to propose solutions to food challenges.

At the USA Pavilion, those who don’t stop and pay attention will surely miss out on its message.

Outside the USA Pavilion, visitors cool off under a fan sprinkler. Pavilion officials say theirs is one of the most popular sites at Expo 2015. (Luca Bruno/Associated Press)

Visitors rushing through, for instance, could easily overlook the Great American Foodscape around the back. That exhibit offers a series of whimsical videos on such topics as America’s food diversity and how immigration has led to cultural and culinary intermingling. There’s a video on how meatballs ended up in spaghetti, making for an Italian American specialty (one that is, of course, considered blasphemy in the fair’s host country).

At the pavilion’s Food Truck Nation, tucked away down a side street, a variety of food trucks serve hamburgers as well as regional specialties such as pulled-pork barbecue sandwiches and lobster rolls. On a recent Sunday, one American patron of the food trucks grumbled about Pepsi products being offered (PepsiCo is one of the pavilion’s many corporate sponsors) instead of Coca-Cola products, while the massive red Coca-Cola Corporate Pavilion beckoned temptingly down the block.

Organizers, naturally, don’t want visitors to focus merely on who the sponsors are — or aren’t. “There are no commercials here,” said Davis, the pavilion’s chief creative officer, sitting on the roof terrace after Nestle’s talk.

More important, Davis said there’s a good reason the USA Pavilion doesn’t have lines forming outside: Organizers worked intensely with a queuing firm after hearing complaints about long lines to enter the USA Pavilion at the Shanghai Expo in 2010. Pavilion officials say that since Expo opened on May 1, drawing up to 300,000 visitors per day, the USA Pavilion has averaged 20,000 to 25,000 daily visitors, making it one of the most popular pavilions despite the short lines.

Up to 300,000 visitors per day arrive at Expo 2015, being held at a site near Milan. (Olivier Morin/Agence France-Presse/Getty Images)

Davis said his team, led by Dorothy Cann Hamilton of the International Culinary Center in New York, fought hard not to stoop to the lowest common denominator in terms of design and not to do anything too “trade-fair-like.”

“We could have had a hamburger-shaped pavilion and a few videos,” said Davis. He said it would have been impossible to avoid having the hamburger represented somewhere — hence its inclusion on the food truck menu — but the aim was to do something more high-minded. “We got no federal money to do this, so we had to be creative. But it also meant we could bring in great designers and do things in a more effective, open way.”

While the USA Pavilion emphasizes substance over gimmickry and freebies, it does try to give people a bit of what they want. Outside the pavilion, a human-size metallic station that spells out the words “I am 1 in nine billion,” with the oversize American flag standing proudly behind it, was especially created not just for reflection or education — but for selfies.

Michelle Schoenung is a freelance writer and translator based in Milan.