This is the Old Melbourne Gaol Crime & Justice Experience. Russell Street used to be the location of the gaol, the magistrate's court, the city watch house and police headquarters, all of which have moved on.
The first part of the gaol was built in 1841, but quickly became overcrowded so a new cell block was built in 1852, and extended a few years later. This is the building that currently exists & I think the left wing on the model. It's based on the Pentonville system of silence and separation. I've read comments that by the time the Port Arthur separate prison was built, those responsible should have known that this approach didn't work, and that was a couple of years before this block was constructed. Did they think the theory behind it was sound, it was just the way it had previously been put into practice that was flawed?
The next wing, at the front of the model, with the chapel and entrance was added about 1860. The west wing, right side of the model, was added a couple of years later to house women. Now demolished, it was apparently a replica of the existing men's cell block.
Later in the century, operations at the gaol were wound down and the place closed in 1924 or 1929 (depending on whether you want to believe their brochure or their website). In WWII it saw use as a military prison for Australian soldiers who were Absent Without Leave. The National Trust took over it in 1972.
So what we have here is three levels of cells, with walkways and connecting staircases at each end.