The path approaches a rocky bluff, behind which the stream runs into a deep, narrow, rock-cut channel.
To the right you'll find a sizeable tunnel cut into the rock, reached by clambering up a rocky slope. Take particular care on the flat rocks in front of the tunnel, and when climbing up to it.
You'll hear the waterfall before you see it but nothing prepares you for what comes next. Rounding the bend, you'll be greeted by a torrent of water pouring down over the end of the tunnel and into a deep pool below.
Having come out of the tunnel - again, take care, retrace you steps towards the beech trees at Pant Melyn.
Take a path to the right that passes through a gap in a stone wall and follow the red waymarkers alongside Nant Gau, where there are more cascades and rock features to enjoy.
GPS will be dodgy however following the sign to the 'cavern cascade' and checking the hint you should be able to find it. I would highly recommend keeping all Geodogs on their leads, as at points there are very steep and long drops to the river. Also this may be a very long and hard walk for young Geokids. Though there are some spots to rest. This cache is on the 'Gentleman's Walk' which is marked by Red Arrows.