Thousands of old bottles - some dating back to the 19th century - have been found at the site of Ballarat's biggest CBD construction.
Construction work on GovHub has been under way since January, with the five-storey building to eventually host 1000 public servants next to Civic Hall.
Nicholson Construction director Richard Nicholson said they had come across a deposit of around 15,000 bottles during excavation, some of them older than a century.
"We were told there was an old cellar (underneath), but I'm not sure if it was a cellar or just a filling-up-a-mine shaft scenario. There's was lot of old bottles over there, none of them full, unfortunately," he said.
"A lot of them were still in shape ... some bottle collectors picked up a few but generally they went straight to the recycling."
Mr Nicholson said they were 40 per cent through the excavation process for the basement, with an eventual depth of 8.5 metres, and had hit the rock layer on the south end of the site.
"We don't quite know how hard that rock will be until we start excavating it, there could be some rock-breaking noise over the coming three months," he said.
"In July we'll start concreting works, we'll then do the two basement levels with concrete up to ground, and then around about September it gets exciting, because that's when the structure starts.
"That's a timber structure, a multi-story timber structure ... November 2020 is the completion date and we're on target to hit that."
Minister for regional development Jaclyn Symes toured the site on Monday.