Via North Egmont: Park at North Egmont Visitor Centre (off egmont road, 30km from New Plymouth). Follow the summit walking track for 1-1.5 hours to Tahurangi Lodge. Head east along the round the mountain track for about 20m, before breaking off onto a small trail that also heads east, but is slightly higher than the round the mountain track. Follow this trail up/east into the organ pipes valley. Some skill at navigation and carefully studying the topo maps beforehand is advised. topomap.co.nz/
is a great resource for topographical maps.