You can’t imagine a President Trump inviting a crowd like this to invade the South Lawn of the White House. Nor, for that matter, would it seem plausible were the Clintons back in residence in the mansion.

But on Monday the nation’s most famous expanse of grass became the stomping ground of a few thousand geeks, techies, nerds, rappers, funk musicians and social entrepreneurs. Or as the civil rights leader and congressman John Lewis neatly summed up the motley crew: “Troublemakers – in a good way.”

It was the first – and you have to presume the last – South By South Lawn. Modeled upon and organized together with the original Austin, Texas, interactive festival South By Southwest, it brought a riot of color to the usually sedate seat of the US presidency.

As a visual statement of intent, a giant placard proclaiming SXSL was erected just in front of the mansion’s back facade. Around it were dotted a series of wooden benches with life-sized figures seated on them created by artist Nathan Sawaya out of Lego bricks in brilliant red, yellow, orange and blue.

In perhaps the ultimate expression of the sense of liberation suffusing the Obama presidency in its final days, the doors to the White House grounds were flung open to those deemed to be using cutting-edge technology as a tool for social change. That was the theme that Barack Obama promoted when he and first lady Michelle Obama headlined SXSW in March, and it was replicated, albeit on a much smaller scale, on the South Lawn.

“The president is saying to the innovators of today: ‘You are great at making things happen, so why not use that power to create positive social change,’” said Hugh Forrest of SXSW, who worked with the White House on planning SXSL.

True to its festival roots, the event also featured some of Obama’s personal musical favorites including a performance by the Denver folk-rock band the Lumineers, who he championed last year on his summer Spotify playlist. The crowd stretched out as the sun went down on red checkered blankets that were handed out to guests, and sang along to the chorus of the Lumineers’ song Ho Hey.

Earlier, the Obama team invited a number of tech startups and creative companies to showcase their wares, with an accent on innovation for social reform. Displays included solar-powered cooking equipment for developing countries, and flexible prosthetics custom-designed by engineers from Olin College in Boston to meet the physical and emotional desires of disabled people.

Among the creative booths, virtual reality (VR) reigned supreme. That’s the nascent art form in which viewers wearing Oculus-style goggles are immersed in total-surround imagery to give them the impression that they have landed in alien territory.

The Guardian’s first virtual-reality film, 6x9, was among three separate VR products and one augmented reality (AR) film on display at SXSL. Directed by the Guardian’s executive editor of virtual reality, Francesca Panetta, in collaboration with creative content studio the Mill, the film traps its audience for nine long minutes within an animated 6ft x 9ft concrete cell of the sort that houses up to 100,000 Americans in solitary confinement at any one time.

SXSL attendees professed to be deeply affected by the film. Hip-hop artist Common said it “blew my mind” while Kara Hollinsgworth, who trains young people for political leadership roles, said it was “very intense – it only lasted nine minutes but I really wanted to get out of there”.

Valerie Jarrett, Obama’s senior adviser in the White House, watched 6x9 and declared it to be “profoundly disturbing. Even though I knew intellectually I was in a virtual reality, it felt quite real. That was nine minutes – I couldn’t fathom how it would feel to be there for 23 hours in a day or for multiple days or even years.”

Jarrett said 6x9 was an example of what Obama and his White House team were hoping to achieve in the last flush of his presidency. “We are seeking to encourage technology that leads to informed change. Technology is a powerful tool that can be used as a force for good.

“We wanted to highlight best practice in the hope that people across the US will look at what’s happening here and engage to effect positive change in their communities.”

Obama has made combating the use of solitary confinement in the US one of the mainstays of his attack on mass incarceration. America currently has more people in isolation cells than the entire prison population of countries such as the UK and France.

In January, Obama used his executive powers to ban the use of solitary for juvenile offenders in federal prisons. Despite the bold move, that still leaves the vast majority of solitary confinement prisoners in isolation under the jurisdiction of state penitentiaries.

“Evidence shows long-term effects of solitary confinement can be deleterious particularly for young people. Using the Oculus and seeing the Guardian’s film can give folks a sense of why that is,” Jarrett said.

The other main focus of the event was climate change. Towards the end of the day Obama emerged from the White House on to the lawn to join the actor Leonardo DiCaprio and climate scientist Katharine Hayhoe from Texas Tech University for a conversation tied to the release of DiCaprio’s new climate change documentary, Before the Flood, which received its US premiere at SXSL.

DiCaprio, who served as the moderator, drew cheers from the crowd when he opened the conversation with a not-so-subtle jab at Donald Trump, saying: “If you do not believe in climate change, you do not believe in facts or in science or empirical truths, and therefore, in my humble opinion, you should not be allowed to hold public office.” (Earlier in the day, Trump named a well-known climate denier to lead his transition team for the Environmental Protection Agency.)

During the discussion, Obama framed climate change as a looming national security threat – and suggested climate deniers lack patriotism. He noted that droughts and changing weather patterns had the potential to displace hundreds of millions of people in vulnerable countries, exacerbating the refugee crisis and sparking new international conflicts. He cited early research suggesting that drought in Syria may have contributed to the country’s extreme civil unrest.

Obama suggested Republicans who don’t take climate change seriously are out of sync with the nation’s military leaders. “We have members of Congress who scoff at climate change at the same time as they are saluting, wearing flag pins and extolling their patriotism,” he said. “They’re not paying attention to our joint chiefs of staff and the Pentagon, who are saying that this is one of the most significant national security threats that we face in the next 50 years.”

With less than four months to go before the Obama era officially comes to an end, the president and his inner coterie are clearly already contemplating life after the White House. “The president is very interested in building momentum outside Washington through change that becomes sustainable. That comes from people, building from the ground up,” Jarrett told the Guardian.

John Lewis, who proudly invoked his record of having been jailed 40 times in the 1960s during the civil rights movement and five more times since he became a member of Congress in 1987, exhorted the young South Lawn invaders to become the non-violent change-makers of the new generation.

“We didn’t have the internet, we didn’t have fax machines, we didn’t have social media,” he said just a stone’s throw from the virtual and augmented reality booths. “But through the actions of thousands of young people in America we made change happen, and now it’s your turn to pick up where we left off.”