The Bridge Valley Deep Shelter is a World War 2 bomb shelter in Bristol – converted from an old railway tunnel. You can read more detailed information on the excellent Forlorn Britain website.
After the war, the tunnel was abandoned again. A few years later, the tunnel was taken over by a shooting club, which closed in 1996 when a handgun ban was introduced in the UK.
Most of the tunnel was lined with metal/waterproofing, but this had been removed in one part. This tunnel section was very damp and drippy!
derelicte 
check out the portsdown tunnels website
I don’t know whether The Tunnel Club in Devizes still exists, or whether it got closed down after the Hungerford shootings, as, sadly, the perpetrator used to use the shooting club. That’s in the old railway tunnel under the castle. The only bit of infrastructure left really. The station area, where I remember going blackberry picking as a child and was probably a wonderful wildlife site, is now a car park and housing estate, and most of the line has either been taken up as back garden extensions or entirely new houses. The cutting that leads from the tunnel along towards Roundway Hospital still exists, as do the bridges over it on Hillworth Road, Southbroom Road and Pans Lane. But, impossible to ever reopen the railway to this town which has probably trebled or quadrupled in size at least since Beeching when the branch line was closed. Now , with large numbers of commuters to Swindon and other places, a railway would be useful.