There isn't anything official. It's not _incredibly_ surprising, I think, that a workplace doesn't have a tourism programme. ;) If no Googler volunteers to give you a tour, no one's giving you a tour.

Google is an amazing place to work. But when loved ones visit, I'm not actually sure what there is to _show_, you know? I mean, there are amusing sculptures (google "stan the tyrannosaurus") and volleyball courts, but we all know that's not amazing. There are great free cafeterias, and snacks in the MKs and on-site laundry and a dozen gyms and .... but come on, now that I've told you that, how much extra value do you get from seeing the gym? Whee, brightly-coloured bikes!

And I can't show anyone the awesome stuff we work on, because it's confidential and besides how would my parents (or whoever) understand why it's awesome, beyond what everybody already knows about Google?

tl;dr: I haven't figured out how to give good tour. Thought at least when guests come I feed them well, on the company dime.