As soon as i posted my last post, i checked the updates below and could see some of the places you had ventured.
A lot has been lost, redeveloped etc but so much is still about and access is usually not difficult.
Did you get to the Clydach gorge area? Some great stuff there.
Some of the first blast furnaces constructed, great tramways, quarries, tunnels....a real treasure trove in a small area for those of us with an interest in IA.