The sale offers discounts on many National Geographic publications. Most items are from previous years but are heavily marked down, even for hardcover editions.
In 2010 the sale will be Friday, Nov. 26, to Sunday, Nov. 28, from 9 a.m. to 5 p.m. Admission is free
In 2004, the sale was held November 26-28.
Everett Daily Herald story about the 2004 sale (registration required)