The campground we stayed at gave us a flier for this so we decided to go along and give it a go. While it wasn't what I expected it was still good and was only $20 so was a relatively cheap tourist attraction.
When you arrive you buzz at the gate and a persons head appears and tells you the cost before welcoming you into the prison. You have the choice of either a historical tour or a ghost tour. I was expecting that there would be a group of people and an actual guide showing us around but you are given a map and a hand held device which you use to listen to the tour as you wander around the prison by yourself. It is interesting seeing the actual prison cells and hearing stories about the prisoners; however as it has been a backpacking hostel it feels like some of the authenticity has disappeared. There are also lots of areas that are closed off and have staff only signs. Some of the prison is quite creepy and it was interesting seeing the gallows where they used to hang prisoners.
If you have an hour or two to spare and aren't worried about spending $20 you may as well check it out.