West Tunnel, Mussenden Road, Castlerock, Co Londonderry, BT51

The West Tunnel is a 283-metre long rock-cut railway tunnel constructed between 1845 and 1852, running through a basalt headland beneath Mussenden Temple, west of Castlerock. It was built as part of the railway line between Coleraine and Limavady Junction, which opened in 1853. The tunnel is one of the earliest of its kind in Ireland and was constructed using the innovative technique of blasting with explosives rather than traditional pick and shovel methods. English navvies experienced in tunnel blasting were brought over by the contractor, Marshall Brothers, to undertake the work. The first blasting operation was ceremoniously performed by Lady Bruce, wife of the landowner. The excavation of some 30,000 tons of rock was required, and a particularly large blast on 6 June 1846 – advertised as 'The Great Blast' – attracted considerable public attention, with steamers chartered to enable spectators to witness the event. The tunnels were blasted through by July 1847 and subsequently lined with brick manufactured at Articlave, near Castlerock.

The tunnel runs in a sweeping curve for 283 metres from the west side of Portvantage Glen to the east end of Downhill Strand, passing beneath the headland that rises directly above it. The structure has relatively few comparable examples in Ireland.

The western portal, located directly below Mussenden Temple at the Downhill Strand end, is semicircular-headed with rusticated and margined abutment quoins and voussoirs that step into the spandrels and feature a plain keystone. The abutments merge into sloping buttresses extending beyond the cliff face. The spandrels and seaward side of the projecting portal section are constructed of random basalt blocks with a rusticated string course above. A low parapet of coursed basalt blocks surmounts the portal, though its coping has been largely replaced with mass concrete. The extrados of the tunnel behind the parapet is grass-covered. Steel wire netting is affixed to the cliff directly above the portal to prevent rocks falling onto the line. A modern metal sign indicates the tunnel number as 197, its length of 283.2 metres, and the location of refuges at 45-metre intervals along its seaward side. Beyond the portal, the railway line continues westwards along a raised artificial platform above the shoreline.

The eastern portal, at the Downhill Strand end of the tunnel, is similarly detailed with a semicircular-headed arch. Its spandrels and parapets are constructed of roughly-dressed random basalt blocks brought to courses, with a dressed horizontal string course running along the base of the parapet. The parapet is coped with advanced dressed basalt blocks. A modern metal sign provides the same information as at the western portal. Steel wire netting is similarly affixed to the cliff above this portal. From the eastern portal, the railway line continues eastwards along a 120-metre long embankment just above the rocky shore to the West Tunnel's paired structure, the East Tunnel.

The tunnel runs through a spectacular setting, passing from the tranquil Portvantage Glen through a high sea-washed headland to Downhill Strand, with the ground above forming part of the National Trust's Downhill Estate. The tunnel has group value with the East Tunnel and shares its history as part of the integrated railway infrastructure of the period.

The line opened in July 1853, completing the route between Coleraine and Londonderry, though through running between Belfast and Londonderry did not commence until 1860, following the completion of the bridge over the River Bann at Coleraine. From 1861, the line was operated by the Belfast & Northern Counties Railway. This company was taken over by the Midland Railway (Northern Counties Committee) in 1903, renamed as the London, Midland & Scottish Railway (Northern Counties Committee) in 1923, and nationalised in 1949. It was subsequently operated by the Ulster Transport Authority from 1949 and by Northern Ireland Railways from 1967. Translink, successor to Northern Ireland Railways, continues to operate the line today.

The tunnel is scheduled as a monument of industrial archaeological interest, with the schedule extent comprising basalt abutments and linings and brick soffits.