Gyfylchi Tunnel.

[lock1999]

Not too much history on this place but Cardiffrail,s site has some info plus there is this report.

http://www.irsociety.co.uk/Archives/25/south_wales_mineral_railway.htm

Explored this tunnel in the 70,s, no pics but an exciting trip as the north end collapsed about 1947 and the tunnel is flooded from about 300 yards in reaching a depth of about 12 feet at the blocked north portal.

The trip was done with wetsuits and air beds and was just a long paddle except for the airshaft at 840 yards which had a large mound of barbed wire and fence posts breaking the water surface.
The water level at the far end being within 4 feet of the arch crown.

I visited this area again in August last year to get a few pics and do a recce for a dinghy trip to the end again, something has changed since the 70,s as there is now a clear tide mark that seems to indicate that the blockage is leaking out, a long dry spell may dry out a lot of the tunnel.

Some pics from the recce.
Portal.
http://i158.photobucket.com/albums/t101/Mondeo2006/IMG_1705.jpg
Curve at entrance.
http://i158.photobucket.com/albums/t101/Mondeo2006/IMG_1265.jpg
Rock and brick section.
http://i158.photobucket.com/albums/t101/Mondeo2006/IMG_1268.jpg
Start of water.
http://i158.photobucket.com/albums/t101/Mondeo2006/IMG_1267.jpg

http://i158.photobucket.com/albums/t101/Mondeo2006/1267Crop.jpg
About 400 yards from airshaft.
http://i158.photobucket.com/albums/t101/Mondeo2006/1266Crop.jpg

If anyone is interested feel free to have a swim/paddle etc, best of luck.