Usually hidden behind bricks and mortar, some of Australia's historic buildings have opened their doors to a curious public. Among them is the Manchester Unity Building - a neo gothic skyscraper.

The Manchester Unity Building is widely considered to be the jewel of Melbourne's Open House scheme. It houses beautiful art deco architecture in the city's central business district.

Described as a slice of Manhattan down-under, it was the work of architect Marcus Barlow. The Aussie came to prominence as an architect during the Great Depression in the 1930s.

Visitors here are overwhelmed by the opulence and authenticity of the interiors.

Constructed in 1932, the building features ornate marble works and multiple elevators which, when installed, were capable of progressing 600 feet per minute.

One of the biggest challenges was installing the glass tabletop designed for the boardroom.

Dr Kia Pajouhesh, building chairman said, "The glass at 320 kilograms0 was too big for construction in anywhere in Australia so they had it constructed in Europe, shipped across and put through the ceiling by crane before the building was completed."

The history lesson continues with a tour through the Phillips Shirt factory, a mid century Melbourne workshop from the 1960s.

It's changed very little, and about a dozen shirt-makers still earn a living here. Originally some 80 machinists would have worked here.

With reams of fabric and piles of patterns, one visitor felt privileged to see this hidden gem.

And to celebrate the 100th birthday of Victoria Police mounted branch, these old stables were included on the Melbourne Open House list. It was built in 1912, but it's still home to the horses which patrol the city today.

Organisers hope to extend the list of open sites in 2013.