The cache is near the bottom of the waterfall, where you get a great view of the water crashing into the pool. You don't actually see the full height of the waterfall from here, so it's well worth climbing up out of the ravine on the opposite side from the waterfall, to get that view. From there you can also get a brilliant view south.
As some people have been asked by the owner of Burnhead Farm not to park there, please use the Parking waypoint provided. From there you can either walk along the road to the farm (although be aware that there are often cows in the field), or follow the track north from the parking point and then bear west.
Congratulations to Jokeroo for FTF!