Ever walked through the diamond district in NYC? An entire city avenue block long but it looks like this place dwarfs even it.

The Pentagon is probably appropriately-sized for America's military-industrial complex and associated bureaucracy. 

The diamond industry I guess enjoys such huge margins on small stones they don't know what else to do with it.

The book describing the history of DeBeers is pretty fascinating if you haven't already read it. The anecdote that still sticks with me nearly 20 years after reading it is the one about how DeBeers pretty much invented and popularized the engagement ring.