If you walk up Birnam Glen and out on to the farmland around Balhomish, you'll find yourself on the path that takes you to Rumbling Bridge in Strathbraan, beloved of Millais and many others since.
Strathbraan is simply beautiful - less commercialised now than it was even a few years ago in many ways, and an absolute must for a drive, walk or cycle if you're in the area. In fact, a fantastic taster on foot or two wheels would be to follow the Birnam Glen path as described above down to Rumbling Bridge, then back via the Hermitage to the River Tay and Birnam.
Glorious - and now you can find out all about this "secret strath" on their new website. I particularly recommend a visit to their picture gallery page.