There it stands: a hulking grey crane, pressed against a blue Sydney sky. The vista is framed perfectly through the rusting bars of an old military guardhouse. This scene of machinery and prison bars is a succinct summary of Cockatoo Island's convict and industrial heritage, which stretches back 170 years. Cockatoo Island (below), located in the heart of Sydney Harbour, has opened its doors to the public. One of the best ways to see it is by tagging along on one of the Sunday tours, organised through the Sydney Harbour Federation Trust. The island sits at the junction of the Parramatta and Lane Cove Rivers. The first thing you notice as you approach from the east is its sheer size. At 17.9 hectares it is easily the largest of Sydney's harbour islands. Tony Harrison, our guide, leads us through the red brick entrance. In the 1830s, Cockatoo was a prison for convicts transported from Norfolk Island. Life was tough. Convicts worked in leg irons, constructing prison buildings and hewing grain silos from the solid sandstone bedrock. In the 1850s the prisoners spent six years creating Australia's first dry dock. The prison was terribly overcrowded. It had only ever been designed for 320 prisoners, however at one stage, it had more than 550. 'This was Australia's version of Alcatraz,' Tony says. 'There was only one man [who] ever escaped that we know of, his name was Frederick Ward, better known as Captain Thunderbolt.' When the prisoners were eventually moved to the city's Darlinghurst Gaol, Cockatoo Island became a ship building and maintenance yard. In the 1890s another dry-dock was constructed. At more than 200 metres long, the Sutherland Dock was the biggest in the world. The dock area was a hub of activity during both world wars. At its peak in 1919, 4,085 people were employed on Cockatoo Island. And between 1857 and 1992, more than 12,000 vessels were docked or slipped at the island for repair or maintenance. 'Generations grew up on the island,' says Tony. 'One woman lived here for 40 years while her husband ran the machine shops and her children went to school across the harbour in Balmain.' The dockyards were decommissioned in December 1991 and all the machinery and equipment was offered for sale. But much of it was too expensive to disassemble and take away, and so it remains, a monument to Australia's industrial heritage. During the 1990s the island was left derelict. Australia's richest businessman, the late Kerry Packer, put in a bid to buy the island on which to build his casino. Developers Lendlease wanted to take over the island and create a new suburb called Cockatoo. But control of the island was taken over by the Sydney Harbour Federation Trust, which is in the process of transforming it into one of Sydney's landmark attractions. This year a boardwalk opened, suspended high along the island's cliff faces. Best of all has been the creation of a landscaped campsite, allowing folks to camp on Cockatoo Island and take in some of the greatest harbour views on the planet. The campsite is already proving popular with tourists, especially for big events like New Years Eve. Revellers donning party hats and drinking champagne, awaiting the fireworks camped on the former penal colony. Now what would the prisoners have thought of that?