Visited with Dweeb a few months back. It was a drab cold Sunday afternoon, perfect weather for a south wales trip.. (It suits the area so well!)
A few people had tours of this place when it closed but it has been off the tourist radar ever since. I had been meaning to go there for literally years but our south Wales trips had always been dominated by various cinema attempts in the past so it always got missed.
Dweeb, having had a tour in the past, was only really interested in the headstock but i managed to make him wait while we crept around the bath house and winding house first. The site is quite compact with security right in the middle so it was fairly tricky to get around all of it un-noticed. The headstock itself was virtually 'suicide'! We went for it anyway and luckily only got spotted by security's 3 legged dog! :p With the pooch yapping away at us and rampantly humping my leg we decided we'd better turn ourselves in and introduced ourselves to the usual ex-miner who was looking after the place. As usual he was sound and said we could look around the outside of the place. Unsurprisingly he did seem to get slightly agitated when we kept appearing in buildings that 'were supposed to be locked' but on the whole very pleasant!
All the other info you need can be found on wikipedia