Box Tunnel

Box Tunnel passes through Box Hill on the Great Western Main Line (GWML) between Bath and Chippenham. The 1.83-mile (2.95 km) tunnel was the world's longest railway tunnel when it was completed in 1841. Built between December 1838 and June 1841 for the Great Western Railway (GWR) under the direction of Isambard Kingdom Brunel, the straight tunnel descends on a 1 in 100 gradient from its eastern end. At the time the tunnel's construction was considered dangerous due to its length and the composition of the underlying strata. The west portal is Grade II* listed and the east portal is Grade II listed. Ammunition was stored near the tunnel during World War II, reusing mine workings. During the 2010s, the tunnel was modified and the track lowered to prepare it for electrification, although in 2016, this plan was suspended.

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).