When I lived in this city many years ago I always wanted to go inside the Clifton Rocks Railway but never managed to gain entry. In recent years a group of volunteers have started making limited trips down the tunnel and I was lucky enough to be on one recently. Small crawl spaces meant no tripod so high ISO is was.
The funicular railway opened in 1893 and carried the well to do from the Bristol Harbour below up to Clifton. It ascends some 60m up the Avon Gorge very close to the Clifton Suspension Bridge. After a short period of profitability the demise of the paddle steamers and trams servicing the bottom station meant the railway fell into receivership and disrepair. However its biggest mark on history was yet to be made.
The masonry is very impressive – I believe it remains the widest brick lined tunnel ever built. Being from the Victorian era it is over-engineered in many respects, not the least of which is the fact that the main tunnel is 6 layers of brick thick. This, and the fact it was under meters of limestone, made it an obvious choice for modification as a bomb shelter during WWII. Blast walls were added along with rudimentary accommodations in the form of stepped seating/bedding.
The bottom section, which is in a very poor state, was actually a secret BBC broadcast facility for South West England. Far more information is made available below by the dedicated volunteers that slowly restore and keep the railway in a traversable state.