When you get to that beach (Hanakapi`ai beach), a great option is to head inland up the river... there's a great waterfall two miles up (Hanakapi`ai falls).
This was one of the most impressive sights I've seen. You can walk right up to the edge (no railings) and look down towards the water crashing against the cliff. You're up so high, that the seagulls flying down by the water look like fruit flies.
So to get here I decided to hump it. Got lost and walked up a mountain and descended into the back of the park. So tired but the view was gorgeous. I would get lost again if I could.