On the market for a staggering $80 million, the historic New York City carriage house owned by John Mack and Christy Mack represents a remarkable investment opportunity. Acquired for $13.5 million in 2009, the property underwent an extensive six-year renovation. Featuring 20 rooms and luxurious amenities such as a wine cellar and soundproof theater, the sale could set a new record for townhouse prices, surpassing the $77.