My mum has the annual pass and she can take a guest in on it free too, car parking is free and cash can be used!
I took my youngest son for a walk there early this year as he had never been (usually walk to Cawthorne) and was surprised you had to pay. We walked from kexborough and entered through the country park entrance. No mention of payment or tickets at this point, only when we got through the 1st field were there signs of tickets only. Spent many a year walking around the park with my mates in the summer months, where the country park and YSP were separate entities. He said to me "Dad what we going to do", just keep walking kid and enjoy the fresh air
There's hidden cameras in the exhibits so that they know when you've been looking at them from the public paths.
I bet these guys are keeping an eye on people sneaking past (with guide dog Penny trying to blend in a couple of years ago).
I've heard if you stand in the middle they shoot lasers out of their eyes at anybody that doesn't have a ticket