how to reach

Lahaul and Spiti can be reached from either the side of Kullu-Manali or from Shimla.
If you come from Shimla, take NH-22 and you will reach Tabo (Spiti). If you opt to go from Manali, the first town will be Keylong, which is also the district headquarters of Lahaul. Though this way remains under snow for around 5-6 months from November to May. One has to cross Rohtang pass to reach Keylong. 

Nearest Railway station is Chandigarh. From Chandigarh you can reach Lahaul & Spiti via Manali or Shimla. 

Nearest Airport is Bhunter in Kullu. It is 160 kms away from Keylong. Bhunter Airport is well connected by flights from Delhi, Chandigarh, etc.