Facebook's Frank Gehry building unveiled in first pictures (gallery)

To get from Facebook Inc.’s existing Menlo Park headquarters to its new Frank Gehry-designed expansion building, you can hitch a ride on a 40-person “people mover” that shuttles beneath Bayfront Expressway. Estimated trip duration? About 40 seconds.

Expect a lot of travel between the two sites, starting today. On Monday, Facebookers began settling into their new offices as the social-networking giant officially opened the structure, dubbed “MPK 20.”

Facebook’s occupancy of the 430,000-square-foot…