"The building itself is pretty simple and isn't fancy. That’s on purpose," Zuckerberg wrote on his Facebook page.
"We want our space to feel like a work in progress," he said. "When you enter our buildings, we want you to feel how much left there is to be done in our mission to connect the world."
Facebook's employees will work in a large room that Zuckerberg called "the largest open floor plan in the world," fitting thousands of workers into the space.
The open room makes it easy for groups to collaborate -- and provides some quiet nooks for meetings. While one meeting room was turned into a ball pit on opening day, it appeared to just be a short-lived prank, according to Instagram accounts of several Facebook employees.
Employees who want to take a meeting outdoors can visit the roof, which includes a nine acre park, trails and various outdoor working spaces.
"Our goal was to create the perfect engineering space for our teams to work together," Zuckerberg wrote. "We wanted our space to create the same sense of community and connection among our teams that we try to enable with our services across the world."