The beauty of Chandratal is incomparable and Cannot be defined in Words.
Route 1 : is from Shimla - Narkanka - Nako - Kaza - Losar -Kunzum Pass- Chandratal , This route is open almost though out the year so If you are going in winter season this is only route available to reach kaza. In winters, It around minus 25 degrees and everything is covered white with snow
Route 2 : It is Via Manali which is also quicker to reach Chandratal. If you only like to visit the Chandratal, This is best route but only opened in Summer Via Rohtang Pass
So from Delhi-Manali- Rohtang pass - Battal - Ghampu - Losar - Chandertal ,same route to back to delhi . you can also take this route while coming if you going from Shimla route , Manali route is shorter and you can easily do it 5 day from delhi to delhi
You can join both route , You can Start from Delhi and reach Chandratal Via Shimla and can comeback through Manali. Or Go from Manali side and Come back from Shilma Side. Shimla route is more scenic and also need more days. Via Kaza, You can also Visit lots of other places like Dhankar Mostry , Gue Mummy, Langza Hikkim( World's Highest post office ) , Comic, Kaza itself, Pin Valley , Mud etc