Andrew, shwmae. 'Sha Nôl, Sha Mlân' means 'Backwards and Forwards' in our local Welsh dialect. It's held on the weekend the clocks change, for one thing. It's also held in a few venues between Ystradgynlais and Ystalyfera. You could read more into it if you want...

You don't need to be able to speak Welsh, but the music is going to be Welsh! There aren't that many Welsh Trad Sessions, even in Wales.
We wanted to put on a session weekend which allowed musicians, who often don't get that much contact with each other, to play together and learn new tunes in a relaxed environment. We're doing some more workshops this year than last, in order to let people who don't have many of the tunes to have a bash at 'em.

The local rugby club have agreed to let us put caravans and campervans on their premises in return for a few quid. Send me a pm if you'd like more details. We've got maybe half-a-dozen vehicles coming already, but there should be room for a few more.

And yes, there are a few Llanidloes boys coming down, Cornelius amongst 'em. Very musical place, Llanidloes.