The usual route to Leh (capital of the Ladakh region) is to ride north on the main highway to Manali about 550kms away, fight for air with a million tourists, have a nightmarish multi-hour ride up the 50kms or so of traffic jams to Rohtang Pass and the eventually start to have fun after that. Not a good plan.
We'll head up the main highway for 4 hours and cut off to Shimla, thus hit the Himalayan foothills in 5 hours of leaving Delhi. Then half way up cut off east and ride via Chail and come out ahead of Shimla, thereby avoiding the main tourist routes altogether right on day one.
We'll swing by the beautiful Sangla valley, then ride through the Kinnaur region in Himalayas proper, swing north along the Chinese border and enter the spectacular Spiti Valley. Through Spiti to the first main pass, Kunzum La at 15000 feet, and drop down into Lahaul Valley. About 90kms offroad through water crossing and melting glaciers and join up the Manali-Leh route near Keylong.
That brings us up to a 1000kms from Delhi, so a 300kms detour to avoid Manali......thus the "long way in".
Appropriately enough, this part of the route comes out like a question mark :)