If you park near the huge refreshment building in Rivington and start walking up towards The Barn pub, you take the very first trail heading towards the Pike on the right hand side. You then walk through an area where trees have been planted in memory of the dead. At the end of that area, you take the first trail on the left........................
Actually it's tough to explain because i'll probably miss a segment of the route out

Anyway it's where they've cut loads of trees down and cleared old stone paved routes that I can't remember seeing before (must have been neglected for years and become overgrown). It's roughly half way up!
Probably the easiest way to find it is where the stone toilets are (walking down from the Pike) as you're facing them with the Pike behind you, you head to your left and take the first trail on the right down - through the tree cleared area and you'll see it on your way down
