Surf's Up dude!
If you're looking for action packed waves which are fun to ride then head to Hanalei Bay. You can spend the whole day in the water. Or if you'd rather play in the sand, the beach is beautiful. It is long and the sand is fine; a good place for walking and running.
Hanalei Bay is located on the north shore of Kauai. It is a very famous beach. Movies were made and many songs have been written about this special beach.
You can also walk to the edge of an old pier and fish or jump into the water.