Used to help at Brockham Narrow Gauge Railway Museum, Surrey. One of the members told me how much was still (then) intact around Blaenau. I got the 1:25,000 OS maps and he pointed me where to go. I came, it turned out to be the first of many trips.
I had previously been in a cave (in Derbyshire) and a tiny mine (near Buckfast, Devon) on a couple of school trips. Which I had enjoyed immensely.
I soon realised there were plenty of holes to look in around Blaenau, so that's what I did from then on.