Worlds longest tunnel above 10,000 Feet which connects Manali to Lahaul Spiti Valley is called:

Atal tunnel

The World’s longest Highway tunnel above 10,000 Feet - Atal Tunnel (9.02 Km) has been built by Border Road Organisation. This tunnel connects Manali to Lahaul-Spiti valley throughout the year. Earlier the valley was cut off for about 6 months each year owing to heavy snowfall. The Tunnel is built with ultra-modern specifications in the Pir Panjal range of Himalayas at an altitude of 3000 metres from the Mean Sea Level (MSL).