Part of the Great Western Colliery, this engine house is open to the public on Saturday 23 and Sunday 24 September.  It can be seen working, powered  by an air compressor.  Hours are  from 11.00 ?  3.00 pm.
Your might even get to run the engine yourself!

Location: 

http://www.britishlistedbuildings.co.uk/300013515-hetty-engine-house-pontypridd#.WbQJd8iGPIU