The Horse Track is an alternative to the official track from Evans Lookout to Junction Rock, in the Blue Mountains National Park, NSW, Australia. There is a good description on the web here, but what follows gives a few extra navigational details, and is correct for March 2013, when I last walked it.
Judging by the absence of signs at each end, it seems that the National Parks and Wildlife Service intend this track to fall into disuse and ultimately disappear. I can see some sense in this: it runs parallel to another, more scenic track that they are currently spending a lot of money on. Still, it's there, it's the easiest way out of the valley, there is one stunning lookout (up a short side track, where the track enters the cliff line), and for those who walk the tracks frequently it makes a change.
Starting from Evans Lookout, walk down the official Grand Canyon track for 15-20 minutes to a track junction where a square hardwood signpost with stainless steel around the top tells you to turn right. Instead, go straight ahead on a clear track not pointed to by the signpost. There is more than one place that fits this description, but if you pick the right one, after a few metres you will pass a yellow metal sign. I forget its exact words, but the gist is "Horse Track. Rough and hard to follow". In fact, the Horse Track is a perfectly good track. It is less rough than the official track, and just as easy to follow. Follow it down, down, down, until you arrive at the main creek, where you meet the official track again and turn left for Junction Rock about 25 minutes away.
Coming from Junction Rock on the official track to Grand Canyon and Evans Lookout, there are two places where you can turn right onto the Horse Track. The first is at a low moss-grown wooden sign about 20 minutes from Junction Rock. It points each way along the official track, but there is an overgrown track to the right that it does not point to. Judging from an old map I have, I think this must have been the original route of the Horse Track. See below for more on this. The second is about 25 minutes from Junction Rock, where there is an old metal sign on a big tree, showing an arrow pointing left. Up to that point you will have had the river on your left; I think the track might cross the river there. Anyway, where the arrow points left, you turn right. Just a few metres in there is a large tree fall. Look carefully for the way through, it bears to the right across some large limbs, not to the left across small limbs and leaves. Don't be discouraged by the fallen timber; get through it the right way and everything after it is easy.
The first right turn after Junction Rock, at the low moss-grown wooden sign, seems to be the original route of the Horse Track. I tried it in March 2013 and got through it, but it's very overgrown and may have vanished altogether by the time you read this. Definitely to be avoided. The main Horse Track, however, was in good condition in March 2013. There were two or three large fresh tree falls, but people were getting through them easily enough.