There are two roads that take you up, the 550 and the 552. Personally, I think the 550 from Waimea has better views.

Keep going past the initial lookout points to the end of the road, which affords you two amazing vantage points to peer down into the Kalalua Valley.

The hiking in adjoining Koke’e State Park is accessible by the same road. The Na Pali overlook trails are beautiful but deceptively hard: you have an easy time going downhill for three miles, but then it’s uphill the whole way to get back. Leave yourself enough time on these trails so that you can get to your car and get out of the canyon before dark.