The walk is about 2km each way and will take about 1 ½ hours (return) at a leisurely pace, or less if you walk a bit faster. The walk is reasonably flat, and although the section of track to Little Congwong beach is sealed, not all of the walk is sealed, and thus is not suitable for a wheelchair or a pram.
With the tree cover the satellite reception can be a bit patchy, so my apologies if the track file does not exactly follow the real track. The real track is mostly very well marked though. The old military pillboxes (as marked on the map) are quite interesting.
There are guided tours of Bare Island Fort (back at La Perouse) on weekends – check the sign at the gate on the island for times and prices.