Nandavan is not too far from Gangotri.I am talking about kalindi khal trek which is about 6000m above sea level.This trek takes you to badrinath and this is also an ancient route from Gangotri to badrinath.
I hope you have made your trip. It would be helpful for travellers if you share the travel details:
1.Route
2.Transportation
3.Weather
4.Budget
5.Places to see
6.Tips for travellers etc.
Happy travelling.