The gradient in the old Victorian tunnel is unusually steep
There are two tunnels under the Malvern Hills - the first was hacked out by hand by Welsh miners and is now the home to a colony of rare bats.
The tunnels go through some of the hardest rock in the country.
This presented a real engineering, and financial, challenge to the people building them.
The first tunnel was completed in 1861, and the second, wider, tunnel replaced it in 1926
The glorious hills almost caused Malvern to miss out on the railway building boom of the Victorian age.
As the great railway lines fanned out across the country there was an obvious need for a line linking Birmingham, the workshop of the world at the time, with the coal fields of South Wales.
The logical route for the line from Worcester to Hereford would have followed the present day A4103 which skirts the northern end of the hills.
The railway had to take the long way round to reach Malvern
This though would have left Malvern off the main line, and the great and the good of the town weren't prepared to let that happen.
They lobbied for the main line to go through Malvern, and that meant a tunnel under the hills.
This was a huge engineering undertaking for the mid 1800's, and the technology of the day meant the tunnel had to be dug, using picks and shovels, by a small army of Welsh miners.
Three air shafts were dropped vertically through the hills, both to provide ventilation when the tunnel was complete, and to allow eight faces to be worked at the same time.
The work, tunnelling through some of the hardest rock in the country, was not easy, and two firms went bankrupt trying to build the tunnel.
The work was finally completed in 1861 by a local engineer, Stephen Ballard, who's family still live around Colwall, at the Herefordshire end of the tunnel.
Coal for the locals
The first train to make the journey was a coal train from South Wales.
This was good news for 100 householders in the village of Colwall, who were given a ton a coal each to mark the opening of the tunnel.
Tunnelling under the hills presented an engineering challenge
The original tunnel is 1,323 yards long and has a gradient of 1 in 23, which is quite steep for a railway line.
There was a law passed requiring trains to stop at Colwall station so that they didn't pick up too much speed in the tunnel.
Malvern's famous water also proved to be both a blessing and a curse.
Water constantly ran into the tunnel as it was being built, but when the tunnel was complete the water was collected and used to refill the steam trains that used the line, and also to pipe water to Great Malvern station.
The navy moves in
As trains got bigger, conditions in the tunnel grew worse for the drivers and firemen on the footplate.
There was only a four inch clearance between the smoke stacks of the largest steam trains and the top of the tunnel.
This meant a very smokey five minutes as the trains passed through the tunnel, and there are documented cases of people passing out on the footplate due to the fumes.
After a partial collapse of the tunnel roof, around one of the ventilation shafts, in 1907 it was decided to build a new tunnel.
The Victorian tunnel closed in 1926, but still served a useful purpose in the second world war.
Bizarrely for land-locked Herefordshire and Worcestershire, the navy took over the old tunnel and used it to store torpedoes.
Now it is the home to a colony of rare bats and only receives the odd human visitor in the shape of engineers making safety inspections.
There have been suggestions that the old tunnel would make an ideal cycle route, though for the moment the bats have the place to themselves.