I’m standing just outside Shimla Station looking at a rather forlorn steam engine. The plaque says it’s KC 520, built in Glasgow in 1905 by the North British Locomotive Company, and retired in 1971.

It still comes out occasionally to puff its way up and down the Kalka Shimla railway — otherwise known as the “toy train” — although these days, diesel locomotives do the heavy lifting.

Built to ferry memsahibs of the British Raj up to Shimla from Kalka, a cool alternative to the steamy plains below, this line is one of the great railway journeys of the world.

When the town became the summer capital in 1864, the final stretch of the journey by horse, camel, elephant, bullock cart and sedan chair took five bone-rattling days. Although the idea for a rail connection was first mooted in 1847, engineering and financial setbacks meant the line was only opened in November 1903.

I start my own journey in Delhi, boarding the early morning Shatabdi Express for the four-hour journey to Kalka. The air-conditioned Executive Class is comfortable and includes a rather delicious spicy breakfast, complete with a few cups of Indian chai.

I cross the platform to board the Himalayan Queen, patiently waiting for passengers, and it’s easy to see how it got its “toy train” name. After the comfort of the Express, the six rows of seats in the narrow gauge carriages are rather uncomfortable. Fortunately I’ve been advised to bring my own cushion.

With 103 tunnels, more than 864 bridges and around 919 curves, the Kalka-Shimla Railway was an extraordinary feat of engineering when it was built. The line climbs 1,500 metres from Kalka to Shimla over its 60-mile length, and the train takes around five hours, passing 18 stations. In 2008 Unesco added it to its World Heritage list.

My carriage is packed with other tourists and the train starts climbing immediately, flanked by hills on both sides. As the engine chugs uphill, I sit by the open window, enjoying the cool breeze and breathing in the scent of pines.

The average speed is around 11mph but on this stretch it’s much slower. In 20 miles we pass four stations and make our first stop at Dharampur, picking up samosas from platform stalls. Ahead I see a cow on the line, just one of the many hazards of train travel in India.

The railway now starts cutting through the landscape in a series of tunnels, the longest almost three-quarters of a mile long. By Taradevi, I’m ready for a change of scenery — and position — moving to the open doorwell, careful to avoid the branches that brush the side of the carriage.

We are now in the foothills of the Himalayas and there are tantalising glimpses of Shimla as the train winds through a series of curves.

Night is falling as we arrive, but I can see the town sprawling over the surrounding hillsides with the original colonial buildings rising to Observatory Hill.

It’s topped with the Viceregal Lodge, the summer residence of the Indian Viceroy, who ruled the Indian subcontinent, home to a fifth of the world’s population, between 1888 until 1947.

A rather dour baronial castle, all turrets and gables in local grey sandstone, it was built to Viceroy Lord Dufferin’s design in 1888 to remind him of home and impress visiting dignitaries.

After independence it passed over to the Indian government. Now occupied by a local university, only a few rooms are open to visitors including the teak-panelled central Hall.

Along Shimla’s main artery, Mall Road, Kipling’s first play premiered at the Gaiety Theatre; recently restored, the half-timbered Tudor style Town Hall is also being spruced up. And Scandal Point, where girls freshly arrived from the UK once made eyes at eligible bachelors, is still bustling too.

It’s 70 years since the Raj ended but its legacy lives on in the Kalka-Shimla railway. It’s just a shame that 1905 steam engine doesn’t get out more.