The clanking of wheels, hissing of steam and the roar of a locomotive as it thunders past - these are music to Hong Kong's railway aficionados.
A group of people from diverse backgrounds, they are united by an interest in all things connected to railways, expressed in hobbies that vary from photography to model building.
Many enthusiasts meet through the Hong Kong Railway Society (HKRS), founded in 1986, to share experiences and plan trips. These jaunts are often to the mainland, where steam locomotives are still in service, although the railway network is modernising rapidly.
'There's romance and nostalgia connected with steam that can't be compared to anything else; it's a display of power from the Industrial Revolution,' says Rickly Wong Wai-ki, who combines his passion for photography with his interest in trains.
He and fellow railway society members Henry Tang Wai-Yeung, Tony Lou Tung-Yuen and Martin Wong Sze-Kin have made many trips to the mainland to ride on and photograph the few remaining steam locomotives.
They've made long treks along railway lines waiting for a train to pass, hiked up challenging trails to secure a good vantage point for photography and even travelled in the front cab with the driver, emerging covered in soot.
Among their most memorable experiences was a trip to southwest China to photograph trains on Beipanjiang Bridge, which spans a 280-metre valley.
'The train takes a number of hairpin bends as it climbs uphill. The driver invited us to ride in the cab, but we opted to trek up the mountain to get a good photograph; I had to lean over a ledge to get the picture,' says Tang.
Railway enthusiasts find most train drivers are very friendly, especially once they prove to be genuine fans. Robin Gibbons, a banker who has made a hobby of studying China's railways, has even shared a crew's breakfast of steamed buns and raw garlic while riding on the footplate of a steam locomotive in Inner Mongolia.
'I remember having to crouch down on the floor when we went through the tunnels,' he says. 'The cab filled with smoke and steam from two locomotives working hard, making it very difficult to breathe - but that's daily life for the crews.'
For Gibbons, the railways also offer an opportunity to discover spectacular scenery. China Rail publicity shots of a train tunnelling through towering rock walls led him to visit the burgeoning tourist destination of Shidu, about 100km by train from Beijing.
Railway enthusiasts tend to be male so the society was delighted last month to welcome Pan Ling, a female guest from the mainland. 'I worked as a trainee attendant on the railway in Guangdong in 2001; that's when I got really interested,' says Pan, who took a holiday to observe Hong Kong's railways.
The fascination with railways usually begins at a young age. Duncan Peattie, a signal engineer, says his love affair with trains started at the age of three when his mother took him to visit a railway station in London.
He became so enamoured he made a career in the railways.
And when work brought him to Hong Kong in 1997 he took a train journey to Shanghai, inspiring a 'labour of love' - an English version of the China railway timetable - that established his name in the railway community.
'I saw a number of trains coming and going and I tried to get more information,' he says. 'It was then that I realised that there was no railway timetable in English. It was very frustrating.'
So Peattie decided to decipher the timetable on his own - a task he describes as detective work matching distances mentioned in the Chinese timetable to locations on the maps. The result is a timetable that has become extremely useful to non-Chinese-speaking rail buffs and tourists.
Unlike other enthusiasts, Peattie is more interested in how rail networks are run than in the engines. 'While around the world the railways are from the past, in China it's still a new thing. It's interesting to see a railway that's doing its job efficiently,' he says.
Rickly Wong, who shares his interest in timetables, explains why. 'You get a sense of the development of the transport system,' he says.
'In the 1921 timetable, for example, it took four hours to travel from Guangdong to Kowloon. Before the Nanjing Changjiang (Yangtze River) Rail-Road Bridge was completed in 1968, all the trains were loaded onto a train-ferry at Pukou and this is reflected in the timetable.'
One of the society's original members, Peter Crush, has become a specialist in railway history after studying pre-1949 Chinese railway history for 25 years.
Crush, who is working on his second book on the subject, has also accumulated a vast collection of memorabilia - from bonds that describe the financing of the railways by foreign companies, to timetables, tickets and photographs.
Prized items include a photo of the Rocket of China, the first steam locomotive constructed on the mainland, and an image of the former railway crossing at Lo Wu. The old steel bridge has been preserved on Kowloon-Canton Railway land next to the new bridge, but unfortunately isn't accessible to the public, he says.
As the Chinese authorities begin to preserve the nation's rail history in museums, Crush has made many tours. He recently took a 27-hour train ride to visit the new railway museum in Kunming.
'Not many tourists know of this wonderful new museum there that celebrates the building of a railway to Vietnam by the French,' he says. 'It's one of the best museums I've seen in China for presentation.'
While steam may soon be a thing of the past, Crush believes trains will remain an important mode of transport in the future.
'Railways are much more environmentally friendly,' he says. 'All short-haul trips should be by rail.'
Wong, who celebrated his honeymoon on a train from Sydney to Perth, agrees. 'We saw gold mines, kangaroos, wallabies and emus; we enjoyed fine dining and met interesting people,' he says.
'You can sit in your own compartment and see scenery go by. You can't do that on a plane.'
For details of Hong Kong Railway Society meetings, go to hkrs.org.hk