Whilst these certainly aren't the highlight of a trip to Belgium they did provide an interesting point of reference on a recent WHS mega weekend around the area.
Our route south pushed us in the direction of Liege, as such our first visit was to the mines at Bligny, the only one of these sites where you can still get below ground. Sadly some unexpected road works led us to arrive shortly after a tour departed. Not really having enough time to wait we wandered around the structures above ground. The most striking was the climb up the slag heap, offering views across the former mining landscape. We also got to see the other attractions Hubert mentions, and like him we weren't especially interested, however the use of former lumps of mining machinery as a crazy golf course was kind of amusing. A quick pit stop in the cafe was the limit of our visit, though it did allow us to see a fair chunk of the local community out for a catch up, which was rather nice to see. This was an enjoyable visit even if we missed the chance to head underground.
A couple of days later we made an unexpected visit to le Grand Hornu. As it was a Monday the main site wasn't open. However, and not for the first time, we encountered a wonderful welcome from people working at a world heritage site. They explained some details, such as the relationship to Mons' role as the current European Capital of Culture, and even the visits that Vincent Van Gogh paid. They even let us head out for a stroll around, which was all we were interested in anyway. It was a pretty impressive architectural ensemble, though its mining functions were somewhat hidden. One of the things I found most interesting was the endless rows of small terraced houses that surrounded the central buildings. These always remind me of my home city, and as such help illustrate the large impact of such sites.
On the whole I didn't feel that I got a full grasp on the heritage of the mining sites; however that was mostly due to my missing the tours and interpretation that was available. These aren't going to top many people’s lists of must see sites in Belgium; however it did give me a better appreciation of the history of this area, beyond the usual views of the glorious cities of Flanders.