Uris Hall
Uris Hall houses Columbia Business School, as well as the Uris Deli and a loud library, the Business and Economics Library.
There are also top secret meeting rooms there, but they're secret, so I can't write about them here. Perhaps the kind of places where one might find Bain Lehman, the bastard love-child of Merrill Stanley and JPSachs.
When it was built, it was so ugly that Architecture students picketed its dedication. Despite an attempted to rein in its ugliness with an addition in the 80s, it remains among the ugliest campus buildings to this day.