The Great Southern and Western Railway (GS&WR) was a railway company in Ireland from 1844 until 1924. The Glenish Viaduct was an Irish gauge (5 ft 3 in) railway. The GS&WR grew until in the late 19th and early 20th centuries, it was the largest of Ireland's "Big Four" railway networks. At its peak the GS&WR had an 1,100-mile network, of which 240 miles were double track.
The Great Southern and Western Railway Company (GS & WR) opened a rail link between Farranfore and Killorglin on 15 January 1885. The line was extended by 27 miles to Valentia Harbour in the 1890’s and formally opened on 12 September 1893.
It served as the main transport system for the Iveragh Peninsula and the last train departed from Killorglin on 30 January 1960. The Laune Viaduct in Killorglin, two tunnels and the Gleensk Viaduct are still standing.