This is a 3,443 yd single track tunnel of the former Rhondda and Swansea Bay Railway between Treherbert (Rhondda and Swansea Bay Junction) and Blaengwynfi. The line opened in 1890 and closed in 1968 as a result of a partial bridge collapse.
The closure was intended to be temporary but became permanent closing an important east-west route.
There is a plan to re-open the tunnel to pedestrians and cyclists Rhondda Tunnel Society .