Archaeologist Jodie Benton has been excavating the earliest perimeter wall of the gaol, which dates back to the 1880s. She's also searching near the northern perimeter wall for the four individuals who are known to have been buried within the gaol.

The excavation is part of the gaol's redevelopment, which is looking at new ways to interpret the historic site.

Dr Benton said the first two trenches had found the wall was in good condition on the southern end of the site, but was less preserved on the northern end.

"It's very evocative to tourists, to local people to be able to see the original perimeter wall that was demolished in the 1890s. It really only existed between the '80s and the '90s because this gaol changed significantly through time, especially in that early phase," she said.

ALSO MAKING NEWS:

The third trench is being used to search for proof of where the four individuals buried within the gaol in the 1800s are located.

Dr Benton said she wasn't searching for remains, she was looking for indications of a coffin or body in the ground.

Three of the individuals who are known to be buried in the gaol were condemned to death, hanged and then laid to rest on site. Another died from illness.

"The only place that all the stories seem to point back to is the northern perimeter wall so we'll give that a whirl and see if we can find anything there. Even if we don't find those grace cuts today it doesn't mean those individuals were buried here it's just that they were buried in different phases so...they could be at different parts of the gaol," Dr Benton said.

Old Dubbo Gaol visitor experience officer Chris Anemaat said they never knew what they were going to discover at the gaol.

"A few years ago we took the roofs off the toilets, which were toilets for the prisoners and found contraband - knives and playing cards. Now we're digging into the soil and seeing little bits and pieces that they're bringing up. It might be a little fleck of glass and even that is interesting, whether or not it was from one of our events we're not too sure," he said.

When the excavation finished on Wednesday afternoon the sites will be filled back in to ensure the space can continue to be used as an area for functions. However, before then everything will be heavily documented.

The gaol has plans to create a new display to highlight the old perimeter wall.

"I've been working for about 12 years and doing the research here. Reading on paper or looking at plans is one thing but to see the archaeological remains, the physical evidence of these things you've heard about is a really powerful thing for us," Mr Anemaat said.