This 1,868 yard Tunnel at Wenvoe first saw active service in 1889.
The tunnel is brick lined except for a short section at its southern end where a change in geology occurs. Towards its centre is a single ventilation shaft, also brick lined and almost the full width of the structure.
Traffic through the tunnel came to a premature close on 31st March 1963 thanks to a fire which destroyed Tynycaeau North signal box. Since then, it has become home to a large water main and extraordinary mineral deposits which adorn the walls. A pile of junk has come to rest at the foot of the shaft and the tunnel now suffers badly from flooding, with waters reaching a depth of four feet after heavy rainfall.
An interesting story about this place is that if the King and Queen were to visit Cardiff or the South Wales area during the Second World War, they and their Royal Train would station here inside the tunnel overnight, this was due the night time air raids during the war. Being inside the tunnel overnight meant that they could remain in peace and not have to be woken up and rushed to an air raid shelter if there was a raid.