1) There is no train from Delhi to Kasol. You can have Volvo from Delhi to Bhuntar and then a local bus from Bhuntar to Kasol. 2)Take Volvo from Delhi to Kullu and then Taxi (INR 500-600) to Kasol. Stay in Kasol camps for a better view n enjoyment, never the less, try for trekking to nearby places like Kheer Ganga, Challal etc Have a safe and wonderful journey ahead.
Weather is pleasant Things to do :
1. Take tour to villages nearby 2. Have some of best Israeli food there (Buddha cafe and Jim Morrison cafe )
3. There are many sites where you can stay like camping basically
4. Tosh village is also great to visit (20 km far )
It's a great time to visit Kasol. I would suggest you to start from Tosh and then come down eventually by covering all the places like Kheerganga, Kalga, Manikaran, Kasol, Rasol and Chalal. The pricing is good enough to travel on a budget just have to find the right accommodation. The food is kinda costly though.