As we've learned from Lauren Bacall's charismatic character in How to Marry a Millionaire, prime real estate is important. In other words, location is everything. Well, what's one to do when the perfect location includes the apartment next door? Why, knock down the separating wall and expand your own haven, of course. Oh, the life of a millionaire. Atop the historic Merchant House in Tribeca, the duplex penthouse is that haven, boasting six bedrooms spread over 6,800 square feet of space. It's so big that different parts of the property are referred to as the north and south wing. There are also 3,000 square feet of private gardens, a professional-grade kitchen, a climate-controlled wine cellar, and a direct elevator. In case you ever want to capitalize on the owners' non-existent buyer's remorse, you should know that the penthouse sold in early 2013 for a cool 15.8 million.