Shillong is just like a heaven. This is the place where you can have lots of fun -- Shillong peak, Wards lake, Elephant falls, Mausmai cave are some of the places where you can explore. You can hire a taxi and can visit this place in a day. I can say that whoever already visited Shillong will never get bored if they visit many times. Please do visit and don't miss out from seeing this beautiful place!
I went to school in Mussoorie when I was in grade school, it's a great place to be at and the wheather is awesome, people are nice and friendly. Everyone speaks English so as long as you can speak English you'll have a great time. It's a place for people who want to go visit hill stations and be able to see the himalayas. It's great, words can explain.
Arambol is the best place in the world -- the people, the music, the fun. Especially if you are there for Carnival you will have a good time. I recommend the hike to Querim Beach -- it's the greatest view. Go to Loekie Cafe, that's where the action is.
Bangalore It's a beautiful city -- not very crowded and doesn't have particular rush-hours. It's a must go.
Madurai It's not the best place for solo travelers as the street hassle is relentless. In two hours wandering the town centre, I was asked for money about once every two minutes, plus there was barely a second passed when there was not at least one rickshaw driver or vendor trying to get money out of me. Sometimes I had more than one person at the same time hassling me. Some of these guys were very aggressive and a firm no several times did not work and I had to yell at them to go away. I have never experienced anything like it even in India.