[ecesena]

Offices: connect people on linkedin and ask, it's surprisingly easy to get a visit to any office in SF/SV. In SF many also have public areas, for example Linkedin, Airbnb, Pinterest.

Founders: it depends. Founders of small startup, same as above. Founders of big/famous startups it's definitely harder.

Go with a more concrete ask though, like I'm doing X, I'm at this stage, I want to understand Y. Then, indirectly, you'll learn more, but otherwise your requests will likely be ignored.