The Map below shows the walking track for the Lower Portals section of mt Barney, the track leaves the car park and ends up at the Lower portals which is roughly 7.2 km return, it is considered to be a moderate to difficult walk and you should allow 2-3 hours walking time. 

You can reach Barney Gorge by continuing along the creek beyond the Lower Portals, you can also get there from the track above the Lower Portals but there is no signs so you can easily miss the turn off and end up heading towards Cleared Ridge.

The Lower Portals