New South Wales (Sydney Region)
Harbour Islands
Two harbour islands, Fort Denison and Goat Island, can be regularly visited on NPWS tours. Fort Denison, a small island east of the Opera House and visible from Bennelong Point, was originally used as a special prison for the tough nuts the penal colony couldn't crack: locals still call it "Pinchgut" alluding to the starvation conditions. During the Crimean Wars in the mid-nineteenth century, however, old fears of a Russian invasion were rekindled and the fort was built as part of a defence ring around the harbour. 
If it's around lunchtime you'll hear the One O'Clock Gun, originally fired so sailors could accurately set their ships' chronometers. Tours are booked from - and meet up at - the NPWS' Cadman's Cottage centre in The Rocks (tel 9247 8861). There are daytime tours (Wed 11.30am & 1.30pm, Sat & Sun 11.45am & 1.45pm; $12; 2hr 30min) and longer sunset tours (Thurs & Fri 5.30pm, Sat 6pm; $14; 3hr), where you get some extra time to relax and enjoy the view - you're encouraged to bring some nibbles and a bottle of wine.

Just across the water from Balmain East, Goat Island is the site of a well-preserved gunpowder magazine complex. The sandstone buildings, including a barracks, were built by two hundred convicts between 1833 and 1839. Treatment of the convicts was harsh: 18-year-old Charles Anderson, a mentally impaired convict with a wild temper who made several attempts to escape, received over twelve hundred lashes in 1835 - and if that wasn't enough, he was sentenced to be chained to a rock for two years in an attempt to break him, with Sydneysiders teasing him as they boated past. Tethered to the rock, which you can still see, his unhealed back crawling with maggots, he slept in a cavity hewn into the sandstone "couch". Eventually Anderson ended up on the penal settlement of Norfolk Island halfway between Australia and New Zealand, where under the humane prison reform experiments of Alexander Maconochie, the abused Anderson made a startling transformation responsibly managing the island's signal station.

The NPWS runs various tours with Sydney Ferries (bookings essential, call 9247 5033), making the most of the island's gruesome history and its present use as the shooting location for the popular TV drama series Water Rats about the water police. Tours range from a Heritage Tour (Mon, Fri & Sat 1pm; $11), a picnic tour (Sun 11.30am; BYO picnic), to a Water Rats tour checking out film sets (Wed noon; $13).

Sydney Harbour National Park
Just 15 minutes from the heart of Sydney are rugged sandstone cliffs, shady walking tracks and secluded beaches. Enjoyable bushwalking for all ages. Hidden beneath the natural heathland of Sydney Harbour National Park lies a fascinating history. Daily tours explore "Pinchgut Island" which was once used as an open-air prison, transformed into a gun battery and adopted as the site for Australia's only Martello Tower, to become Fort Denison. Special tours explore the historic Quarantine Station (above) and the tunnels and gun emplacements that were also once part of the Sydney Harbour Defence system.

At La Perouse the historic Cable Station (1882) houses an Aboriginal Art Gallery and the worldclass La Perouse Museum, commemorating the voyage of the French Navigator La Perouse.