The tunnel is 2 miles and 241 yards long. Its maximum depth is some 290ft and it measures 25ft 6in high by 25ft wide. It was built to carry the Leeds & Thirsk Railway (later the Leeds Northern Railway, now the Harrogate Line) under the ridge between the valleys of the Aire and Wharfe rivers.

The larger tower of the northern portal was at one time used as a residence. The southern portal (SE242408), near the Leeds and Bradford airport, is plainer in design but still quite striking.

It was a difficult tunnel to construct. It cuts variously through hard sandstone, shale and clay, and there are seven major faults in the rock near the centre point. Some 2,300 men and 400 horses were employed in building it, and 1,600 million gallons of water had to be pumped out.

The tunnel has a gradient, falling to the north. Four of the original 34 cutting faces were made into permanent ventilation shafts measuring 40ft by 30ft -- wider than the tunnel itself.

contractor: James Bray, Leeds