In the hills behind Craig-y-Nos lies Penwyllt, a former industrial community, now with the remains of a Victorian quarry, and the railway station formerly on the Brecon line, where Adelina Patti used to alight.

You can view additional information on Penwyllt, and a selection of photographs on Ystradgynlais Info's webpage on Penwyllt.

The railway buildings are remarkably well-preserved, and the trackbed leading off in both directions can still be walked. Penwyllt is also a popular destination for walkers and lies across several walking routes.