As the title says, buy one (adult) entrance to the races and get one free. Prices seem to start at £13.00 per ticket, depending on which course you choose. (Bearing in mind kids get in free in most courses, you can get a family of four in for £13.00, quite a cheep day out as long as you don't have a bet and lose!!!)
There are 39 different courses from Brighton to Perth offering 130 different race days when you can take advantage of this offer. You have to complete a short questionaire from the attached link before you go to the booking page.
Surprised this hasn't been posted before as the promotion has been ongoing for quite a while.