Support for historic Port Arthur walls

Former inhabitants of Port Arthur's historic penitentiary probably spent years wishing the walls would fall down.

But authorities have just spent millions making sure the iconic Tasmanian building at the World Heritage site remains upright.

After being closed for almost a year, the popular tourist attraction in the state's south will reopen to visitors on Saturday.

Huge steel upright beams now support the former jail's walls, and previously inaccessible areas are open to visitors, revealing original window joinery, remnant glazing and plastered finishes.

The famous penitentiary ruin, which dates to the 1840s and was once Tasmania's largest building, has been the focus of a $7 million conservation project.