MPK 20 is the first building on Facebook's new campus to open for business, though it will take some time for employees to move in.
Totaling more than 430,000 square feet, it's a massive structure that will ultimately hold about 2,800 people.
The landscape team has planted some 400 trees on the roof, and Facebook hopes it becomes a haven for local bird species.
Over the weekend, Facebook invited a group of top Bay Area Instagrammers to get a sneak peek at MPK 20. Here they are posing on tree stumps on the roof garden.
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They also gave us our first look at some of the amazing custom artwork Facebook had installed inside.
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Facebook worked with 15 local artists to achieve the new headquarters' colorful look.
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This part of the building has plaint splattered on the floor.
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The building is one open room, with winding staircases that lead between floors.
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Architect Frank Gehry describes his collaboration with Mark Zuckerberg: "He did not want it overly designed. It also had to be flexible to respond to the ever-changing nature of his business; one that facilitated collaboration and one that did not impose itself on their open and transparent culture."
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This hallway has a stunningly orange glow.
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Since the main room is so large, meeting rooms are situated in large glass enclosures in the center.
And here's a look at another piece of art that was custom-made for the office.
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One Facebook employee posted this picture of a swinging teepee on the roof.
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This looks like a great place to take a break.
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The roof also includes a half-mile walking path that winds around in a loop.
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