If you're looking from the perspective of celebrating Shivratri, then go to Mandi. Mandi's Shivratri is the most famous in whole of Himachal. But if you want to go to relax, then Tirthan valley is a good option.
You Can Visit Isha foundation, Coimbatore. They have huge Aadi Yogi (shiva) Murti and organize for this day on a grand scale. Its an absolute pleasure to be there.