It's not a dinner party. Instead,
underground dinners are a gathering of random guests, sometimes in
costume, at a venue kept secret until the last minute with a menu tied
to a theme. Should P&V do this in New York City?  I think that it would be a terrific holiday party idea. The surprise adds to the fun.

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http://www.dailyworld.com/article/20090927/NEWS01/909270321