Last time Hilton had a “Resort Escapes” promotion it was for a free night certificate after certain number of nights. This time, however, it is just a fifth night free by booking a special rate plan PGRES1 or RE1. You can access Hilton’s web page for this promotion here.
This offer is valid for bookings made between March 15 and April 30, 2013, for stays up to September 30, 2013. Note that you need to book at least 14 days before you arrival date to get this rate. Hilton also charges one night deposit, although this rate is cancelable until 7 days before scheduled arrival.