West side of the beach is known for water sports, especially surfing, and a small coral reef
Spot dolphins & whales, if you visit in December, you may spot turtles laying eggs too.
Hire a boat and go fishing with the locals near the coral reef.
Enjoy a relaxing Ayurvedic massage in Ayurveda centers in Mirissa
A river safari would definitely money well spent as you could see nature at its best, well spread out paddy fields hovered by migratory birds and water animals are definitely a treat to eyes.
Pic credit :dronepicr/flicker