Lloyd's in London. Not the bank; the insurance underwriters. The system is very much like the medieval system: negotiations and transactions are all done in cubicles in a face-to-face way. We couldn't go in; no one but employees can.
This building is an example of "modernism" at its best. Modernist architecture is simple and functional. This is so functional that it doesn't even have walls. The stairs, heating pipes, lifts, and even washrooms are outside of the main building; there is no facade enclosing the building in this way. It is also self-sufficient; they use heat exchangers to heat or cool the building without drawing on electricity.