Cenarth Falls, Y Gerwn, Tresaith Waterfall/Gwalia Falls, Clydach Falls/Sgwd Clydach.
West Wales (or Southwest Wales, or whatever you want to call it) is easily overlooked when it comes to waterfalls, and with good reason; it has less relief, more marshes and flat estuaries, without the rivers being able to drop far enough to make waterfalls that anybody cares about. But what it lacks in normal-style waterfalls, it makes up for with some alternatives. It has a lengthy coastline, with extensive sea cliffs. Typically, the streams dig deep little valleys between them that slope steeply without interruption to the sea, but occasionally streams (never rivers) tumble over those cliffs, creating tall spouts in odd locations. Several can only be seen from out at sea, or poorly from above.
Most of my knowledge extends over the short length from Aberaeron to Aberporth, and various parts of the Pembrokeshire coast, where it is obvious that most residents and visitors do not care too much about the waterfalls - most have no names, and are only around 10 metres tall at most. And the waterfalls are no better. (Yes, that was a joke, whether you found it funny or not.) Examples include those north of New Quay, or at Trwyn Crou (seen on the dolphin-spotting boat trips). However, from the tourist hotspot of Llangrannog to the lesser-known Tresaith, there is a small patch where a couple of the waterfalls are named (not very imaginatively), and the coast paths offer some nice routes to them. Due to tidal influence and lack of daylight, the relevant part of this gallery was taken in segments over a couple of days, but it is presented here as a continuous gallery.
This must not be confused with the waterfalls in the Clydach Gorge, which are at the far end of the Brecon Beacons National Park. The Clydach Falls are at Neath Abbey, Neath, right by Swansea, on the River Clydach, in Cwm Clydach (AKA Glynclydach), in the Dyffryn Clydach Community. Not the River Clydach at Clydach in the Clydach Gorge, nor the River Clydach near Talybont-on-Usk, nor the Afon Clydach joining the Sawdde on the Black Mountain, nor the Afon Clydach near the Usk Reservoir, nor the Clydach in Cwm Clydach joining Cwm Treweryn by Sennybridge, nor the Nant Clydach in Cwm Clydach joining the Usk near Sennybridge, nor the Afon Clydach near Brechfa by Carmarthen (or the nearby Cloidach), nor the Afon Clydach in Cwm Clydach joining the Afon Nyfer in Pembrokeshire, nor the Nant Clydach at Clydach Vale near Tonypandy, nor the Nant Clydach in Cwm Clydach that joins the Taff near Pontypridd, nor the Clydach Brook 10 km upstream along the Neath, nor the Upper Clydach River which joins the Tawe at Pontardawe, nor even the Clydach River which joins the Lower Clydach River in Cwm Clydach that joins the Tawe just 5 km away at Clydach, but the River Clydach that joins the River Neath at Neath. It's obvious, really. Really ... no, really. Despite its name, it's not even a proper waterfall. Only the bottom part is natural, while the top is a weir. Why is it even listed here? Because it is. Shut up.
To get there, take the A465 to the Neath junction and pick up the A4230 heading West. Just after crossing the river (you might not notice that), take Longford Road on the right, towards Neath Abbey. After passing under a railway bridge, there are three paths heading down on the right to the river-side path, and there is a layby a short way after the last one. Take whichever path you want - this gallery assumes the last one before the layby, which is almost directly above the main waterfall. The entire stretch of river shown here is just 250 metres long, so you may want to continue some distance upstream along the footpaths just to add a little more interest, or a little downstream to visit the ironworks.