Hi Amlan, Sri Lanka is one under-rated tourist attraction, you should visit for sure! A few places to visit when in Sri Lanka:
1. Colombo: Spend some time on the beaches, visit the Kosgoda Sea Turtle conservation project 2. Scuba Diving in Hikkaduwa 3. Misty hills and tea plantations of Nuwara Eliya 4. Hike to Adam's Peak
5. Visit the World's end at Horton Plains National Park To know more about Sri Lanka including Hotels, restaurants, activities, you can follow this itinerary: https://www.tripoto.com/sri-lanka/trips/places-to-visit-in-sri-lanka-tourism-itinerary