Rocky Ponds is a series of waterfalls, cascades and pools along Tank Creek, culminating in a final 30 metre drop to a small sandy inlet on the Hawkesbury River. There are several access options but none are easy and involve a lot of walking (or perhaps cycling) and/or boating and climbing.
Option 1 is to start from the Parking Waypoint on Woy Woy Road and follow the Tunnel Fire Trail to the start of the Rocky Ponds Fire Trail (trackhead T0). Turn right onto this trail and, a further 3.6km along, turn right again onto the Highway Ridge Track (trackhead T1). This last track is quite rutted, so if coming by bike it's best to secure it here and continue on foot. The total distance is 8km each way but there's little in the way of elevation change until you reach the Highway Ridge Track.
Option 2 is to take the ferry from Brooklyn to Little Wobby wharf (reference point R0) and follow the Pacific Trail, Defile Track (trackhead T2) and the Midway Ridge Trail (trackhead T3) north to the ponds. This is only slightly shorter than Option 1, though, and the climb up the Defile Track is quite steep. Be aware also that this route passes through the Broken Bay Sport and Recreation Centre and you'll need to obtain a (free) hiking permit by calling 131302 (see this NSW Government Office of Sport website for more details).
Option 3 is to come by boat to the sandy inlet below the final falls and follow the faint walking track up on the left of the gully. There's a rock face along this track that needs to be scaled and there used to be a rope to use here, but last I heard it had gone so this might no longer be a viable option. UPDATE: crash2079 has reported that there's now a new rope in place, as well as another further along near the waterfall.
Whichever way you come, you'll need to bring plenty of water (at least two or three litres) and pick a cool day. This is not a cache to do if the temperature's much above 25° C. Take heed of any fire danger warnings, as there's no escape route (other than by helicopter) in the event of a fire.
There's a fairly well defined track that leaves the Highway Ridge Track at trackhead T4, beginning on the southern side of the creek and going past the first small waterfall (reference point R1). The track crosses over to the other side of the creek just above Jeanies Falls (reference point R2). A side track leads down to Jeanies Pool (reference point R3) which is a good spot for a swim if it's not too cold. Continuing along the main track brings you out at trackhead T5 onto a broad rock shelf that the creek flows across and over the Final Falls (reference point R4).
To reach the cache, head up the hill on the southern side of this shelf to a large honeycombed cave in which it's concealed (see hint). The container is a black low-profile Duratech instrument case and includes a pencil and sharpener.
Congratulations to crash2079, the first to traverse the ponds!