Apollo I visited Inverary jail last month on my way back from Oban and i can only echo what you say. me and ms Glasgowgub found it fascinating seeing the cells which were only about 8ft by 8ft , there was also in the courtroom a reconstruction of a trial going on. it was interesting to see the "exercise area" in the yard- this consisted of a concreted surface about 7ft by 4ft surrounded at the sides and ceiling by a cage. I imagined the prisoner to be like a human exhibit in some sort of bizarre zoo!( must have been the few pints i had in the hotel next to the jail :wink)
Seriously though its a cracking place to visit and its less than a tenner for two and you also get to see some stunning views of Loch Fyne