Me and my mum decided to go and do the four falls trail near brecon a few months ago. Going in the week is definitely a good idea for photography, we only saw 3 or 4 people all the way round. Also going after a good amount of rainfall means a decent amount of water flowing.
Of the four falls, Sgwd Isaf Clun-Gwyn (which is the third of the falls you get to) is my favourite. Its also worth noting that although its the third fall you get to, its the second fall down the river, as you need to double back on yourself to get to it. Be careful, it is a bit iffy to get to this fall, there is even a warning sign telling you not to carry on! But keep going, its worth it.
I took quite a few pictures in this location, but this is by far my favourite.
Details of the Four Falls Trail can be found here.
Camera: Sony A6000
Lens: Sony 10-18mm @16mm
Shutter Speed: 1 Sec
Support/Tripod: Giottos Memoire 50
Post Processing: All in ON1 Photo RAW 2017. Modules including Dynamic Contrast, Colour Enhancer, Vignette (Big Softy) and Sharpening.