Murphy and I found this yesterday whilst out on the Welsh Coast path. We had to leave the marked path because it was completely flooded with mud which had been washed off the ploughed fields. The tunnel is under the mainline from Swansea to Carmarthen. I must have been over it countless times on the train into London. On the other side of the the tunnel in the distance you can see the far bank of the river Towy. We had a great walk although we had to shelter soon after I took this in an abandoned Dutch barn from a heavy shower. Next time I do this walk I will wear my gaiters over my walking boots, bring my waterproofs and my DSLR.