Any good management consultant knows there are two reliable, quick and easy indicators of the nature of the culture of a large organisation: reception and any kitchen area. Your welcome and handling in the former gives you first impressions. Courteous and proactive? Or not. The kitchen area is more subtle and in the larger firm with several such areas can indicate the mood in various silos the organisation has inadvertently formed. Who's hanging around? What are the topics of conversation? Who is talking about who? Behind their back? What's the biggest issue...who used my mug?
You don't need a 20 page report to summarise your culture, just drop in unannounced in those two hot-spots. And learn.