This is the back of the Courthouse. (See front here.) If you've been naughty and on remand, you are delivered on a van that goes inside this cage; they shut the cage before you're let out the van.
But that's just my theory. Police is to the left, just behind where I was standing, and I do know there are basement cells there, because I read it in the paper... Soooo.... they wouldn't transport the baddies just to cross the drive way, would they?