There are many islands in Karnataka, It is very calm and cool place.
Basavaraj Durga Islands - This is an island in the Arabian sea near Honnavara. It has number of fresh water wells. You can reach this place by boat with the help of fishing travelers, By a sail upstream on a river Sharavathi, Hindu Temple is also there in the top surface which is built between 16th and 17th centuries.
Kurumgad Island - It is in the shape of tortoise in Arabian sea. You can reach this place by boat jetty from sadhashivagad. On the backwaters of RIver Kali at Karwar. This island is 1km from Devbagh beach. Which is easily accessible from karwar. Palm tree along the coastal line and sight of the grey sea looks superbly amazing!
Netrani Island - It is located close to Murudeshwara, On a beach between Honnavar and Bhatkal This place is largely famous for Snorkeling and scuba diving, during June - September.
St. Mary's Island or Coconut Island - It is a set of 4 small islands in the Arabian Sea, It is Off the coast of Malpe in Udupi, It is idylic with swaying palms, fine white sand and black polished rocks that frame its coast. The Rocks are quite stunning that offers a great view from the top.
Uppina Kudru Island - It is a small island village located 6-7 km north of Kundapura. Once served as the center of trading for salt and sea food. Today the place is occupied with Several ancient temples and mutts, There is something surely about this temple, And the feel is absolutely soothing being on an Island, Sometimes it is needed to disconnected from the world and spend sometime embracing the nature to its fullest.
These are truly adventurous places.
Souce - Metrosaga