Robert Johnson writes that "Mark Zuckerburg's presence seems everywhere within the 1 million square feet of office space spread over 57 acres of land, and he's often seen walking around like everyone else during the workday.Because of that there's a slight expectation that he'll stroll around the next corner, or out from the frozen yogurt shop along the Main Street-themed heart of campus."

Notice the word "HACK" in the middle of the campus.

"HACK is blocked out in sprawling letters on the ground at Hacker Square, outside the building called Hacker Company where Zuck holds these infamous brainstorming group sessions, according to our guide Jackie Rooney. Multiple walkways painted the same color orange as the Golden Gate Bridge connect the Hacker Company with surrounding structures."

Zuck's office is there at the bottom, with the signs "PLEASE DO NOT PHOTOGRAPH THE ANIMALS :-)".

Andrew Bosworth on "Working with Zuck":

https://www.facebook.com/notes/facebook-engineering/working-with-zuck/339013388919

"The Hacker Way" at Facebook:

http://www.startuplessonslearned.com/2012/02/hacker-way.html