Kauai is my favorite Hawaiian island, the one I keep going back to. Kauai is green, full of wilderness, not overly full of tourists (except in the Poipu Beach area, which can be avoided), has great hiking and river kayaking, and its old volcanic mountains have been eroded by the very large amount of rain into stunningly beautiful landforms. Here is a bit along the road somewhere in the northeast quadrant of the island.