Severn Tunnel
The Severn Tunnel (Welsh:Twnnel Hafren) is a railway tunnel in the United Kingdom, linking South Gloucestershire in the west of England to Monmouthshire in south Wales under the estuary of the River Severn.
The tunnel was built by the Great Western Railway (GWR) between 1873 and 1886. It is 4 miles 624 yd (7,008 m) long, although only 2 ⁄4 miles (3.62 km) of the tunnel are under the river. For well over 100 years it was the longest mainline railway tunnel within the UK, until the two major High Speed 1 tunnels (London East and West) were opened in 2007 as part of the Channel Tunnel Rail Link. It takes approximately 3 minutes 40 seconds to travel through the tunnel.