The publisher George Newnes made his fortune launching popular magazines like Tit-Bits and The Strand, the latter giving Arthur Conan Doyle his first Sherlock Holmes serial. He had money to spend, and a taste for engineering. After commissioning the Lynton and Lynmouth Cliff Railway on the north Devon coast, he turned his attention to Bristol. He wanted to connect Clifton, the elegant suburb on top of the gorge cliff, with Hotwells below, where the paddle steamers landed, the Bristol Port Railway terminated, and the Bristol Tramways had their southern terminus. A surface route was impossible. The cliff was too steep. So Newnes hired George Croydon Marks, the same engineer who built Lynton and Lynmouth, and they tunnelled straight through the limestone. The 28-foot-wide bore was driven by both machine drills and hand drills, then lined with brick. It took two years and cost £30,000, three times the original estimate.

The railway ran 450 feet through the cliff at a gradient of 1 in 2.2, which is to say almost 45 degrees. Two cars were attached by a cable running over a pulley at the upper station. Both cars had large tanks underneath them. At the top, a reservoir filled the upper car's tank with water, making it heavier than the loaded lower car. Released from its brake, the heavier car descended, pulling its lighter counterpart up. At the bottom, the water was emptied into a lower reservoir and pumped back to the top by a pair of Otto engines installed at the foot of the tunnel. The whole system was, in effect, a closed loop of water doing the lifting. Passengers paid their fare and rode in carriages that climbed or descended by no force more violent than the weight of a few hundred gallons of water shifting downhill.

The opening day attracted 6,220 passengers. The first full year saw 427,492 fares. For a steep tunnel in a damp seaside city, those are extraordinary numbers, and they reflected something Bristol genuinely needed: a fast vertical connection between the riverside trade district and the comfortable houses of Clifton. But the numbers slipped. By 1908 the operating company was bankrupt and was sold for £1,500. In 1922 the city widened Hotwell Road into a major arterial called Portway, which killed the tram connection at the bottom and shut the Bristol Port and Pier Railway station. With no passengers arriving at the lower terminus, the funicular's customer base evaporated. The last train ran on 29 September 1934, forty-one years after the first. The water stopped flowing. The cars stopped moving.

The tunnel did not stay quiet. During the Second World War, with German bombers regularly over Bristol during the Bristol Blitz, the BBC moved part of its operations into the dry, bomb-proof shaft inside the limestone. They built broadcasting studios in the tunnel and used it as a backup transmission site safe from air raids. Some sections also doubled as an air-raid shelter for nearby residents. The BBC kept using parts of the tunnel until 1960, well after the war ended. A volunteer group has since restored sections of the upper station, including the BBC studio rooms; in 2019 plans were announced to convert the top section into a permanent museum. The cars are long gone, but the tunnel itself, brick-lined and steep, remains exactly where Marks and his drilling team left it, a forgotten artery still running through the heart of the Avon Gorge.

The Clifton Rocks Railway tunnel runs almost vertically through the eastern cliff of the Avon Gorge, with its upper station at 51.4540°N, 2.6255°W next to the former Grand Spa Hotel (now the Avon Gorge Hotel) and its lower station at river level beside what was once Hotwells railway station. From the air the tunnel itself is invisible, but the line is roughly directly under the Clifton Suspension Bridge approach on the eastern side of the gorge. Look for the small upper station entrance near the bridge's east tower. Recommended viewing altitude 1,500-3,000 feet. Bristol Airport (EGGD/BRS) lies 7 nautical miles south.