Which Indian railway, opened in 1903, climbs from Kalka to Shimla through the Himalayas?

The Kalka–Shimla Railway is the Indian mountain railway that climbs from Kalka to Shimla through the Himalayas.

The line opened in 1903 during the British colonial period to connect Shimla, the summer capital, with the wider railway network at Kalka. It is a narrow-gauge railway running for about 96 kilometres through steep Himalayan terrain.

The route is known for its many curves, tunnels, bridges and hillside views. It rises from Kalka at about 656 metres above sea level to Shimla at roughly 2,076 metres. Small trains still operate along the historic line.

UNESCO included the Kalka–Shimla Railway in the Mountain Railways of India World Heritage group in 2008. The Darjeeling Himalayan Railway and Nilgiri Mountain Railway are also UNESCO-listed Indian mountain lines, but they serve different regions and routes.