no direct train from chennai to shimla..... u need to reach kalka or chandigarh from chennai,as there is only 1 train from chennai to chandigarh,u may come to delhi first then take a train upto kalka n from kalka u can go for the metre gauge train or bus upto shimla...but the metre gauge train will be an awesome experience,as it passes thru hilly terains,mountains...will be an great experience