Repairs have been carried out on one of the country's deepest railway tunnel shafts to stop water cascading into it.
Cowburn Tunnel, in Derbyshire, lies on the Hope Valley Line between Manchester and Sheffield.
Network Rail said the £800,000 repairs had seen a sophisticated system of drainage pipes installed.
A spokesperson said it was a "privilege" to work on the structure, part of which is known as "the cathedral".
Because of the tunnel's remote location, construction materials were airlifted into position by helicopter and engineers built a temporary lift platform to work from, using winches and pulleys.
Network Rail teams were lowered into the ventilation shaft in a custom-built cradle, similar to their Victorian predecessors who excavated the shaft 127 years before them.
Trains could still run in the tunnel below during the work.
The shaft is 791ft (241m) deep which, if it were a building, would make it taller than Canary Wharf in London.
Dennis McGonnell, Network Rail's works delivery manager, said: "It's a huge privilege to keep heritage structures like Cowburn Tunnel in good condition for rail passengers and freight and it's amazing to see up close the quality of the Victorians' workmanship.
"We work on a lot of structures in remote locations but working in a tunnel this deep and using helicopters to get materials to site is rare.
"It makes you realise what an amazing feat of engineering building this tunnel and ventilation shaft was all that time ago without the modern machinery we have today."
The tunnel between Edale and Chinley goes underneath landmark hills including Kinder Scout and Mam Tor in the Peak District National Park.
- The tunnel was engineered by the Midland Railway, with the shaft constructed in 1894 over the course of two years
- The shaft opens into a large chamber which is known as "the cathedral" because of its pristine stonework
- Why such precision was used to build it is a mystery to railway engineers as it is usually in the pitch black and rarely seen by anyone
- However the ventilation shaft also inadvertently acted like a huge drainpipe with water from the land above cascading - in the words of Network Rail - "like a massive shower head" on to the tracks below
- The new drainage pipes collect the water to protect the 127-year-old brickwork
Source: Network Rail