If you are in Kerala, then you can check out these places in your 3 4 days trip.
And if you are in Tamilnadu, then you can check out either of these places.
1. Conoor and Ooty or
2. Kodaikanal, Isha Adi Yogi Centre (Coimbatore) and hogenakkal falls
I think Om beach near gokarna would be a good option for three days. There are a two other beaches that connects from Om beach. the way to the other two beaches is a hike basically next to the ocean. the half Moon beach and the paradise beach. it's definitely worth a shot.! three beaches three days 🤙
April is not a good time to travel to South India as even in hill stations Mercury is at its peak hovering between 35 to 40 degree Celsius. The second reason as April is the starting of summer vacation in South most of the places will be crowded and if you are looking for a peaceful vacation chances are rare that you get any. Come to South Post Monsoon or during Monsoon.