The Dinas silica mines are...... I guess, if you've not seen them then you might want to, but the bits of machinery are few & far between. It's the kind of place you'll find iPhone explorers, even dog-walkers in. There's a kind of a through trip in there, that is to say a walk-through trip, and this can be arranged to go up the waterfall gorge if anyone fancies getting wet.
Trying to think what else is in the area, for the silica mines - certainly at the rate most UCET trips go - won't take long. Garth iron mine is not far away, with (Andy Farrow will NEVER forgive me for not mentioning this first time around!) a place for an epic SRT drop for which 60m rope is almost certainly inadequate.
Also in the area are numerous small coal levels which go to bad air / roof collapses after a few hundred yards.
Oh and some weird things called caves. Don't know what they are.