I played 36 at Old Head a few years ago and it was tremendous. Two groups of 4 played 18 around noon, had lunch and beverages, and then we all played 18 more starting at 5pm (course was empty and we carried, no caddies this time). The weather was almost magical -- warm, sunny, very slight breeze. the course was nearly empty. With a few holes to go, they sent out a cart asking if we would be staying for drinks and dinner (yes!). I've played 36 holes a day on higher "ranked" courses, but never had a better 36 hole day than that one.