I havn't been, my cert is expired. I hear it is neat, everything was abandoned when the mine closed. So there are desk with paper on them(yes underwater), mine trucks, etc...
It is big enough to get your open water cert in, so don't expect anything tiny.
The place that runs it is:
West End Diving Centers
:: Welcome to West End Diving :: Professional Diving Centers Since 1960 ::
12464 Natural bridge Road (State Highway B, not 243 that runs into the city)
That is the location of the dive shop. (used to be a Hardees) Behind the Machinist Hall and Target.