After visiting Boom Boom Again, return on the west side of the leat. There's an old quarry here where stone was gathered for making the buildings of the gunpowder works. Gorgeous Glade on the other side of the river is another quarry, which apparently was used for lining the channel of the leat.
The cache is a small L&L at the S end of the quarry. No scrambling or climbing needed! Search carefully please!
Onward! To reach the next cache in the series, King o'the Hill, continue south briefly. Just before reaching the remains of a gunpowder building, go right (SW) up the bank on a small pathlet heading away from the leat path. See the route map. Follow the high pathlet until it joins a bigger path, turn right. For the unobservant and geographically challenged, a waypoint is given for the start of the pathlet! ;)