The ceremonial unveiling of a $12.5 million multipurpose park and adjacent pavilion this weekend at the Oshman Family JCC in Palo Alto will complete a campus that has been a decade in the making.

The project, which includes an artificial-turf field surrounded by a walking/jogging path as well as a firepit and audio hookups for concerts, films and other large-scale events, originally was planned for the JCC’s grand opening in 2009 — until the Great Recession changed those plans and delayed it until now.

The field, which has nearly as much area as a football field, has been in use since early July and is part of what is officially called Freidenrich Community Park. The other part of the project is called Arrillaga Family Pavilion.

The official opening is Sunday, Aug. 12, with a celebration that will feature carnival games, a magic show, water slides, Zumba classes and music. A ribbon-cutting will occur at 12 p.m., followed a load of activities and entertainment, finishing with a performance by the Jewish party band Shamati from 2:15 until 3 p.m. A full range of fitness activities from yoga to kickboxing to an adults-vs.-kids soccer game will take place on the new field, and there even will be free 10-minute chair massages.

Sally Kauffman Flinchbaugh, chief operating officer of the JCC and the person in charge of the project, was strolling around campus last week when she saw a woman with a walker on the jogging path as kids in a summer camp kicked balls on the new field.

“That’s success. That’s what we’re hoping for. It’s really what the JCC should be, a gathering place for all ages,” she said. “When they actually start interacting, that’s even better.”

Zack Bodner, the JCC’s chief executive, called the park a “transformative space” that can host everything from Shabbat gatherings to outdoor concerts to events such as Burning Mensch, the JCC’s “tribal celebration of Lag B’Omer.” He is looking forward to putting up a giant tent for a community Sukkot meal in late September.

“I think people are looking to do Jewish different these days than they used to, and we’re going to give them a space to do that,” he said. “We live in one of the best places in the world climate-wise, so why not do more things outside?”

When funds dried up a decade ago, the envisioned park became nothing more than the roof of an underground parking structure. So the rest of the $300 million campus (including the $150 million Moldaw Residences, a continuing care retirement community) was built and the idea of an outdoor green space languished.

Until a few years ago. That’s when the Freidenrich family donated half the $10 million needed to complete the park and pavilion, and Silicon Valley real estate billionaire John Arrillaga vowed to get construction done in one year. The project ended up costing about $12.5 million, Bodner said, with Arrillaga covering $2.5 million out of his own pocket.

The S.F.-based Jewish Community Federation donated about $750,000, as well.

Starting the work last July and pushing it through to completion in a year was important because John Freidenrich, an attorney and venture capitalist who also was a major donor to Stanford University, died last October. Also, rebuilding from the Sonoma County fires has consumed most of the Bay Area’s construction workers.

“If we hadn’t started it last year, it might not have happened,” Bodner said.

The park will give neighboring Kehillah Jewish High School, which already uses the JCC’s gym and swimming pool to host competitions, a place for outdoor sporting events. The JCC’s preschool and camp programs also will be frequent users.

The park also will provide the 8.5-acre Taube Koret Campus for Jewish Life with some much-needed green space. A plan to landscape the main walkway through the campus — which was part of the original blueprint — remains on the JCC’s to-do list.

Bodner said adding greenery, including the new park, will make the campus — which hosts about 25,000 visitors a week, officials say — a place people are more likely to gather or hang out. When he arrived at the JCC five years ago, Bodner said it was not a welcoming space.

“It was a little too cold, too concrete, too corporate,” he said. “It was very transactional. People would come to work out and they’d leave, they’d come to drop off their kids and they’d leave, they’d come to hear a program and then leave.

“One of the visions we had is that gathering spaces matter. It’s that sense of community that gives you a sense of meaning in life.”

Arrillaga Family Pavilion and Freidenrich Community Park Grand Opening Festival. 12 to 3 p.m. Sunday, Aug. 12 at Oshman Family JCC, 3921 Fabian Way, Palo Alto. Free. (650) 223-8656 or paloaltojcc.org.