It is available on all islands. Kauai has some of the most beautiful trails in the world. Diamond Head near Honolulu is a medium family hike with a beautiful view of ocean and island all in one. There are hundreds of hikes available with varying degrees of difficulty. Maps and books are available at any book or outdoor store.
Water activities are popular here.
There are no private beaches in Hawaii with the exception of those that are on military property. Beaches are free although parking or camping may require a fee. Surfing, fishing and diving are amongst the most popular water sports. All are available in one way or another but may require equipment and or training. Caution should always be used in and around the ocean.