Fortress Canyon is a nice canyon, though not particularly deep or dark. It is best visited in warm weather as there are a number of long swims. The lunch spot at the end of the canyon is a highlight, looking across to Lockley Pylon at the top of the cliffs above Govett Gorge. The walk out also has superb views.
Driving west along the Great Western Highway, take the main exit to Leura. Turn right at the roundabout, and then right at the first street. Head down the hill and turn left at the roundabout. The road does a couple of sharp bends after 700m, and becomes unsealed. Continue for another 6km to a parking area at MGA555726. Park your car here.
Walk west along the fire trail. Ignore a turn off to the left after 600m. At a clearing after 1.5km, continue past an overgrown fire trail and on to a foot track. At the top of the ridge after about 500m, turn right on to a track that leads down the ridge to the NE, and follow this down to the creek at MGA554746. Follow the creek downstream. Eventually you need to start wading, and this is probably a good spot to put wetsuits on if you are using them.
There are a number of sections of canyon. The first very short section starts with a short climb down or careful jump, and a 20m swim at about MGA553747.
After opening out for some distance, the second section starts with a 2m jump at around MGA546750, and several swims.
The abseil is shortly into a third section of canyon. This is about 6m. It can be jumped, but the depth is usually only about 2m, and there are rocks that need to be avoided.
There is more swimming to the end of the canyon. Just past the end of the canyon, Fortress Creek goes over the cliff into Govett Gorge in a 70m waterfall, which is a spectacular spot to have lunch.
Head back from the edge of the cliff about 50m and look for a track up the gully to the south west. This leads up to the Fortress, and then back along Fortress Ridge until you rejoin the fire trail you started in on.