I remember doing this years ago, then we went with huge heavy packs and ran up the hills Bugger me! it's either moved a lot further away and grown in height or I've got older.... yeah that would be it then.
Not the easiest of the waterfalls to get to, indeed it's a bit of a bastard the way I went.. I started at Dinas rock, follow the path up the left side of the rock and keep to the left where the path splits, eventually you reach the top, but it's a lot of climbing uphill and uneven ground in places, then theres a boggy patch, not dangerous just messy if it's been wet.
You'll come to the top of the path down to the falls after an hour or two, now this used to be horrible big steps all the way down, now as parts collapsed there a zigzag path down part way and then you join the old steps, sadly the bottom of the steps is the same, missing in fact, it just goes to bare broken and slippey mess that needs care crossing, then your at the bottom with a good view of the falls.
Now you can go behind these falls but care is required as it's very slippery and theres always the risk
of falling rock from the overhang above, indeed it was closed for some time due to safety concerns. So approach at your own risk, keep in mind your a LONG way from any help if anything happens.