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!