THE family needed an outing last weekend and I managed to get them to Lartington in Teesdale before they rumbled that they were really on the look-out for more old things.

This time we were searching for the remains of the Deepdale viaduct, a mythical, spidery creature which was once to be found lurking in one of the dale's deepest gorges.

The South Durham and Lancashire Union Railway left Barnard Castle, went over Percy Beck, crossed the Tees and then came into the village of Lartington where there was a junction. The Tees Valley Railway headed north to Middleton-in-Teesdale; the larger line headed south towards Bowes and then over the Stainmore summit - the highest railway in the country, I believe, and probably crossing the most inhospitable terrain.

It opened on August 8, 1861 - exactly 150 years ago. I feel a little guilty as I've rather neglected it. Its prime mover was Henry Pease - I got a whole supplement out of his other great 150-year-old project, Saltburn, but have barely mentioned his crowning railway.

The railway trackbed south out of Lartington is nicely tarmaced but isn't a footpath so the walker is sent through a cows' field, down a dip into a boggy morass out of which a footbridge miraculously rises. Then you climb back up the other side until you have to turn 90 east and are plonked onto the nicely tarmaced railway trackbed. It is almost as if someone, somewhere is deliberately making it awkward for visitors with dodgy knees, like me, to enjoy the Teesdale countryside.

The reason the trackbed is nicely tarmaced is that it leads to a remote terrace of houses, Cat Castle Cottages (it wouldn't have harmed anyone to allow the footpath to run all the way along the trackbed). The cottages were presumably connected to the adjacent former Cat Castle Quarry.

As we neared the quarry, the trackbed ran through the rock cuttings and sidings veered off to the west onto the old quarry floor.

Just after the third siding, an old signalbox arose out of the vegetation. It is terribly tumbling down and has several old doors and strange pieces of sticky-out ironwork that really need some explanation. Sadly, I know none. I don't even know why Cat Castle is called Cat Castle.

I found this quote from Fletcher’s Picturesque Yorkshire of 1903: "Some distance along Deepdale the Traveller will find a pile of frowning rocks rising high above the surrounding foliage, this is known as Catcastle, but there is no local information as to the meaning or derivation of the name."

I am not alone in my ignorance.

A few yards south of the Cat Castle signal box, Thomas Bouch's spindly, spidery viaduct crossed the deep dale of Deepdale. It was 740ft long and 161ft high, and impossible to imagine. So deep is the dale that it must have been an exhilarating treetop route.

The northern abutment of the viaduct can still be seen, on an extremely slippery footpath that pedestrians share with a 4x4 track.

I'll have to return when the vegetation has died down because I am intrigued about the tunnel that appears to run through the abutment, because I wonder what remains of the southern abutment and because the view to the bottom of the deep dale must be truly astonishing.