The Rhondda Heritage Park (or The Welsh Mining Experience as it now markets itself) is located in the former Lewis Merthyr colliery.
There is a café and play area on site but access to the main buildings is by guided tours only, and very good they are too.
Although mining on the site dates back to the 1850s, the current buildings date from the sinking of the Bertie shaft in 1880, and the Trefor shaft in 1890. The winding engines for both shafts survive and are particularly impressive.
For opening times, ticket prices, etc. please see the official web site detailed below.
Things get a bit more problematic, when the tour moves into one of the adjoining buildings, and we descend into the 'mine'.
This is achieved by a disguised slow moving domestic lift that, in actuality, takes you down one floor. Here there is a reproduction of a mine gallery. It's very well done but, inevitably a bit warmer and dryer than the real thing. If you are in the Blaenavon area, visit the Big Pit for the genuine article.
The tour ends when we ascend to the surface via a run-away mine cart simulation. Apart from the problems this gives me as a one-time physicist, it also introduces a theme park ride. For me, there is a danger that, in Dysneyfying the appalling conditions that the miners worked in there is a risk of trivialising their suffering. Still if it helps attract the kids, it can't be all bad, I suppose.
External Links and References
Welsh Coal Mining Experience, Rhondda Heritage Park
The official site, with details of the opening times, cost of guided tours, etc.
Include a video of the runaway mine cart in which the narrator attempts the world record for the most uses of the word 'experience' in different contexts in the shortest possible time. https://www.rctcbc.gov.uk/EN/Tourism/RhonddaHeritagePark/Home.aspx