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.