Wenvoe tunnel at The Black Mountains

This is a large tunnel running underneath Culverhouse Cross in Cardiff. We paid it a visit this weekend, and it turned out to be quite a treat! Arrow-straight with a single airshaft halfway along, it turned out to be easy to find, only a short walk from the car park, and (if you look hard enough) very easy to get into despite being fenced off. But the most remarkable thing about Wenvoe was the mineral formations that had formed inside…

Background

Work was started on the Wenvoe tunnel in 1888 by the Barry Railway Company as a direct link down to Cadoxton and Barry docks. In 1898 the tunnel was completed and in full use. It was, and still is, one of the longest tunnels in south Wales at 1867 yards, a shade over 1 mile long. The tunnel was closed in 1964.

Getting there

How to reach the north portal from M&S car park, Celverhouse cross

Getting to, and into, this tunnel proved to be no great challenge; parking in a remote corner of Marks and Spencers car park at Culverhouse Cross retail park, we set off north. Having crossed over a fence and a small field we found ourselves in a pleasant woodland on a winding path. After less than five minutes we stood at the brim of a deep, oval cutting, the northern portal somewhere below. A slippery descent lead down to the flooded cutting, bright green weeds and algae thriving in the still water. Our first thought was that the fence was completely sound other than a missing spike above the lock, and we would have to climb it, but closer inspection revealed one of the fence slats to the left of the gate was loose, and could be rotated around to let us squeeze through with only a minimum of embarrassment; I knew that eighth round of toast was a mistake.

Inside

As mentioned before, this tunnel is dead straight (with a gradual ascent from the north portal). It is wide too, double track all the way. This makes it look deceptively short, but believe me, after five minutes progress into the dark you’ll swear the south portal isn’t any closer! a large water main runs the length of the tunnel and makes an excellent causeway to keep out of the damp. Except for the very southernmost portion of the tunnel, both walls and roof are neatly lined in brick. There are no bulges, cave-ins or repairs evident. The most striking features in my opinion were the calcite and rust deposits that have formed on the walls, some are truly amazing, some looking very much like miniature versions of the pools formed by salt deposits at hot springs, in Colorado for instance. A very good example of natures tendency to adopt similar growth patterns on very different scales. We also saw curtain stalactites forming on the curved walls, jet black secretions and thick rust build-up, and some portions of the wall were completely encased in calcite.

At the 46 chain mark, a mighty airshaft dominates the tunnel. It is very big, almost the entire width of the tunnel, and looking up it gave me a little vertigo. Enough light spills down it to be able to turn all torches off whilst nearby, and directly below it a huge pile of assorted junk has built up. It’s hard to say how deep the airshaft is, but I’d estimate about 25m.