I did this walk with the L family from church.  Drive from Weston Creek via the southern suburbs through Tharwa.  Take the Naas Road, then Boboyan Road.  After passing the turnoff on the right of the Old Boboyan Road (signposted Yankee Hat car park) the road soon becomes unsealed.  Stop at the lookout a couple of kilometres on to take in views of the Gudgenby Valley.  Continue a further 5km to the signed parking on the right for Yerrabi Trail/Boboyan Trig.

Yerrabi Trail is number 12 on the Namadgi National Park map, Walks on walking tracks.  It is rated 4 km return (2 hours), but can be completed a little quicker than that if so desired.

We picked up a great brochure and set off through the wet trees down the gentle slope to cross Little Dry Creek.  Then on up the track to the Mount Boboyan Trig, 1459m.  According to the Environment ACT Namadgi Guide and Map, one can 'enjoy magnificent views of the Bimberi Wilderness'.  Not this time - fog and mist enveloped us and we could only see 20m in front of our noses.  A 10 minute stop for snaps and we returned.  We then drove to the Yankee Hat car park.

Yerrabi - Distance: 2.7km  Time: 9.50am-11.00am, with a 10 minute stop.

Another very informative brochure is available.  The day was still overcast, but the peaks of the Bimberi Wilderness could be appreciated.  This is a lovely little walk, suitable for almost anyone (certainly a family with kids or older folk).  A bit dry looking in winter (I've walked it since and it is beautiful on a Spring morning).  The track crosses a delightful wooden bridge over Bogong Creek and there is a further length of boardwalk.  Then open grasslands, a patch of remnant eucalypt forest and the rock on the lower slopes of Yankee Hat.  The aboriginal rock art is excellent - a place to reflect on their culture and heritage.

Yankee Hat - Distance: 5.9km  Time: 11.30am-1.40pm, with a 15 minute stop.