Four decades after its conception, artist Michael Heizer’s Levitated Mass is finally open to the public. A 21-foot boulder looming over a concrete trench, the installation allows visitors to walk beneath the massive, 340-ton rock. The boulder made a historic and much-chronicled trip through four counties over 11 days in March on its way to the Los Angeles County Museum of Art (LACMA) from a quarry 60 miles east of the city. On Sunday morning, a crowd of more than 1,000 people gathered at the museum to watch the sculpture’s unveiling.

Attendees listened to opening remarks from LACMA director Michael Govan, board co-chairman Terry Semel, Mayor Antonio Villaraigosa, and L.A. County Supervisor Zev Yaroslavsky before the ceremonial ribbon was cut and visitors streamed into the trench. Situated behind Renzo Piano’s Resnick Pavilion on LACMA’s campus, the sculpture will be free for the public to visit.

While Heizer first sketched the land art piece that eventually became Levitated Mass in the 1960s, it wasn’t until he found a boulder in Stone Valley Quarry near Riverside, California, in 2005 that met his requirements that the piece started to become a reality. LACMA raised $10 million in private donations to finance the project and construction on the trench began over a year ago.

Fanfare around the transport of the giant rock turned the route into a raucous block party for the last leg of the logistically complicated journey, but placing the boulder above the trench was also a complex engineering feat. In a region susceptible to frequent earthquakes, the museum had to ensure the stone would remain stable during a seismic event.

The design and engineering team had to balance Heizer’s vision with the safety of the public. “We had to figure out how not to compromise the aesthetics of the artist,” says Ron Elad, associate at the L.A. office of Buro Happold Consulting Engineers. They inserted nine 18-inch steel rods into the boulder to ensure it wouldn’t overturn during an earthquake. Additionally, the team installed steel wedges on both sides of the rock to prevent it from sliding sideways. Two concrete triangles stabilize the walls underground, on either side of the boulder.

The result is an artwork steeped in paradox, simultaneously weighty and ethereal. It manages to appear both natural and manmade at the same time. And as Govan pointed out to the crowd, echoing a sentiment expressed by the notoriously reclusive artist, beyond its experiential contradiction, “How often can you see the bottom of a sculpture?”