India's longest train journey, the Vivek Express, connects Dibrugarh in Assam to Kanyakumari in Tamil Nadu, covering around 4,188 km in approximately 75 hours. The journey takes passengers through several states, from Assam's tea gardens and the plains of Bengal to the cities of Odisha and Andhra Pradesh, before reaching the greener landscapes of Kerala and the southern coastline. Here is what travellers can see along the route and how to plan the trip.