Taken from
www.nwa.com when searching for flights to DTW:
Originally Posted by www.nwa.com
Earn Double WorldPerks Miles now thru June 30, 2004 when you stay at the spectacular new Westin Detroit Metropolitan Airport with direct access to Northwest's new WorldGateway terminal. Mention Promo Code N2YTIP when booking and present your WorldPerks number at check-in. Book Now
The 'Book Now' link directs you the hotels website. Nice deal if its combinable with the 6000 spg bonus.