I’m not sure of the legality of the track which runs along the culvert – its just marked as a ‘path’ on the OS map but I’ve never had any grief from riding it – loads do.
As per Tony’s instructions about though, when you get to the left hand fork (marked by a BW post IIRC) at the end of the culvert, if you go left then its a nice little flowing descent into the top of Luddenden Dean. You’ll get to a cross roads – left continues to drop into Luddenden Dean but if you turn right/back on yourself, that BW loops over the top of the moor and there are a couple of options of dropping straight into Peckett Well village (unlike Tony’s route which drops you off near the ice cream van on the Oxenhope road). Once in the village, you can drop over the road in the Peckett Well BW down into Hardcastle Craggs…
All in, from Ogden car park, the cheeky bit under the wind farm, around Warley Moor res and then across the moor and down to Hardcastle Craggs is (IMHO) one of the best 5/6? miles of trail around… Especially when its bone dry.