If you're walking through Birnam Glen, it's well worth a little diversion to find this delightful waterfall. From the bridge that crosses the burn before entering the Ladywell Plantation, you can simply follow the burn for a few hundred yards until you reach the falls - but be aware there is no path and the walking is rough, with steep scramble at the end.
Alternatively, cross the burn by the bridge and take the left fork in the forestry track, follow that for a few hundred yards and you will come to a point where they have been clearing the forest. The falls are just below here.