During summer months in each city on island is possible to find good offer of all kind of water sports including Banana Bus, Parasailing, Water Ski, Slider, Fly Fish, Speed Boat, Stand up Paddle.
More about watersports available on this links:
Semi Submarine excursion
Interesting excursion with semi submarine from port Krk. KK 300 is a boat designed to look like a real submarine, including the conning tower, external steering and rounded shape of the hull. On the world exists only about 55 similar vessels. Semi submarine has the highest ratio of window to the traveler, it's small and nimble that it can take you in the best position for sightseeing. It do not dive below the sea surface, it has an underwater cabin with large bulletproof glass windows, which is located 1.5m below the sea surface. More information here
SAND AND TIME. Sand sculpture park.
For the first time, in summer 2015, one of the most picturesque places of The Balkans, its Adriatic Sea Coast of the Croatian island of Krk will host a sand sculpture exhibition, "SAND&TIME Krk Summer 2015", which will run under the auspices of the Association of Ice, Snow and Sand Sculptors and the administration of the town of Krk. The festival is set to be held in an open air space, over 3,000 square meters in size, in the major town and the capital of the largest island in the Adriatic Sea, Krk. You will have a chance to enjoy sculptures and composition made of sand; creations which could be called a real piece of art., with a limited lifespan. Hurry up to get your chance! And at the sunset you will get a unique opportunity to enjoy and become a participant to "The Light Show" and the "Sand Art Show".
More information on offical web site.