Originally known as the Portnalls Number One Railway Tunnel and served the Bristol Port and Pier Railway’s Hotwells Branch with six trains running throughout the week. The tunnel extended for 175 yards under what now is the Bridge Valley Road. When Great Western and Midland Railway a joint venture in to extend the lines from Bristol Temple Meads and the South Wales lines owned by GWR; this caused the traffic on the Bristol Port road to be greatly reduced. By 1921 the line had been totally abandoned south of the Sneyd Park Junction; it was eventually pulled up to make way for the construction of the A4.
After the line had been abandoned, the tunnel was forgotten about until the start of World War Two and the air raids on all major British Towns and Cities when it found a new use as a Public Shelter. The tunnel quickly gained the reputation of being the safest place to be when the siren sounded and bombers headed in; at one point so many people were heading to the tunnels each night that the council had to forcibly evict the people seeking refuge and begin a pass system. This caused much resentment amongst the local population, but the blitz passed and the tunnel was once again abandoned.
In the later part of the 20th century the tunnels were taken over by the Bristol Gun Club for use as a short range. In 1996 when hand guns were banned the Club closed and the tunnels abandoned again. Within the tunnels there are a number of interesting features; the first third has been converted by the gun club, the central third exposes the original rail tunnel and the final third displays the shelter.