The correct answer is Lahaul-Spiti.Atal Tunnel:On October 3, 2020, Prime Minister Narendra Modi inaugurated the Atal Tunnel Worlds Longest Highway Tunnel in Manali, Himachal Pradesh.The 9.02 Kilometre Long Tunnel has been constructed by Border Roads Organisation (BRO) at a cost of INR 3, 300 crores.It connects Manali and Lahaul-Spiti Valley. Important PointsThe Tunnel is built in the Pir Panjal Range of the Himalayas at an altitude of 3000 Meters (10, 000 Feet) from the Mean Sea Level (MSL).Prior to the construction of the Tunnel, Lahaul-Spiti valley was cut off for 6 months due to heavy snowfall.It reduces the road distance between Manali and Leh by 46 kilometres and time by about 4 to 5 hours, and the distance between Manali and Keylong (Himachal) will be reduced by 3-4 hours.The South Portal (SP) of the Atal Tunnel has located a distance of 25 kilometres from Manali and the North Portal (NP) is located near the village of Telling, Sissu, in Lahaul Valley.The Tunnel can withstand a traffic density of 3, 000 cars a day and 1, 500 trucks a day at a maximum speed of 80 Kilometres Per Hour.