East Tunnel, Tunnel Brae, Castlerock, Co Londonderry, BT51

The East Tunnel is a 614-metre long rock-cut railway tunnel constructed between 1845 and 1852 through a basalt headland just west of Castlerock. It is one of the earliest such tunnels in Ireland and was constructed using the relatively innovative technique of blasting with explosives rather than traditional pick and shovel methods. Work began in October 1845 under the contractor Marshall Brothers, who brought English navvies experienced in tunnel blasting. The first ceremonial blasting operation was performed by Lady Bruce, wife of the landowner. A particularly notable explosion on 6 June 1846, when approximately 30,000 tons of rock were blasted away to create the passage through the headland, attracted widespread attention and was advertised as "The Great Blast". Chartered steamers brought spectators to witness the event, which was compared in contemporary accounts to the explosion of the chalk cliffs at the Shakespeare Tunnel on the Dover railway. The tunnels were finally blasted through in July 1847 and subsequently lined with brick manufactured at Articlave near Castlerock. The line between Coleraine and Limavady Junction opened in July 1853, having been constructed by the Londonderry & Coleraine Railway Company. From 1861 it was operated by the Belfast & Northern Counties Railway, which was taken over by the Midland Railway (Northern Counties Committee) in 1903. The company was renamed the London, Midland & Scottish Railway (Northern Counties Committee) in 1923. Following nationalisation in 1949, the line was operated by the Ulster Transport Authority and from 1967 by Northern Ireland Railways, with Translink continuing operations today.

The tunnel runs in a straight line from the west end of Castlerock to the east side of Portvantage Glen through a high sea-washed headland. Despite its utilitarian function, both portals exhibit a degree of embellishment.

The eastern portal comprises a semicircular-headed arch with rusticated and margined abutments, quoins and voussoirs. The voussoirs step into the spandrels and have a plain keystone. The spandrels and parapets are of roughly-dressed and coursed basalt blocks. A dressed horizontal string course runs along the base of the parapet, the top of which is sloped to follow the line of the road crossing at this point. The parapet is coped with irregular stones but has been heightened with mass concrete following the road gradient. A small enamel plaque at the left end of the string course identifies this as bridge number 196. A modern metal sign notes the tunnel as 614.05 metres long, with refuges positioned every 50 metres along its seaward side. Galvanised metal poles run up each side of the portal; they were probably for electric cables but now appear redundant.

The western portal, at the Portvantage Glen end, differs only slightly from its eastern counterpart. Its spandrel is of random basalt blocks and the string course over is chamfered along its top edge. A low parapet of coursed basalt blocks sits above, with projecting basalt coping blocks. Sections of the parapet and coping have been repaired with mass concrete. The cliff directly above this portal has been gunited with sprayed concrete, and steel wire netting has been affixed to its face to prevent rocks falling onto the railway line. From the west portal, the railway line continues along a 120-metre embankment just above the rocky shore to the east portal of the West Tunnel.

An air shaft, originally approximately 280 metres in from the eastern end of the tunnel on open ground, was designed to vent smoke from steam trains. It is now subsumed into a caravan park, capped over with reinforced concrete with a small manhole for access should the need arise.

The tunnel has spectacular setting through its juxtaposition of cliff and sea and possesses group value with the West Tunnel. Both tunnels are explicitly cited on 1848–52 Ordnance Survey six-inch maps and later editions. The line is of industrial archaeological interest and also holds the status of a monument. The tunnels were scheduled in December 2016.