The Kalka-Shimla Railway was included in UNESCO's World Heritage list in 2008 as part of the Mountain Railways of India. This narrow-gauge railway, built in 1903, is an engineering marvel featuring 102 tunnels and 864 bridges. The other options - Dilwara Temple (famous for architecture but not UNESCO-listed), Bhiterkanika Mangrove Area (not a UNESCO site), and Vishakhapatnam to Araku valley railway line (scenic but not heritage-listed) - are not correct.