Get Landranger OS map 170. There are a few BOATs either side of the Afan valley. Just east of Aberdulais you've got the start of Sarn Helen, which I think is still open during the months of June, July and August to Dyffryn Cellwen. I think the other sections of Sarn Helen are closed now. You could easily run into trouble on these lanes so best not to go alone unless you know what what a Landy can and can't do and you yourself really know what you're doing and have some recovery gear.