I used to go that way every year, to a motorbike rally near Llanddeusant, and after you pass all the Tawe villages and Brynamman you come over a pass with a really twisty descent, much used by tossers on TV car shows. At the crest of the pass there's a quarry (marked Herbert's quarry) off a side road, and the place is/was shaped just like a stage and auditorium. Views to the north are stunning.
I used the rally as an opener in my novel 'Cold feet' and I fictionalised a road crash there for 'Ride On'. Oddly, the real crash was one I was most unfortunate to see on the A82 by Lochan na h'Achlaise. Car, boulder, front-hinged bonnet sheared and driven back through the windscreen, unbelievable quantity of blood. I spent a while in the first place I could pull over before I was well enough to ride on.