About 8/10 mile past mile marker 16 on the Hana Highway, a bridge crosses Palauhulu stream (the same stream that empties into the ocean at Ke'anae Peninsula below). Beneath the bridge is a series of pristine (sapphire) pools that you won't be able to view from the road.
Access is via two trails on the makai side of the bridge before you cross it. The trail immediately next to the bridge is very steep, very difficult, and should be avoided. A bit further to the left of the bridge, about 50 feet over is a large tree. There is a trail here too, and it's significantly easier to get down to the pools this way.
A few of the pools are mauka of the bridge in a constricted gorge that flushes the water through at a very quick rate. Use caution swimming here. A small water chute (falls) empties into a lower pool makai of the bridge. Never dive into this or any other pool at this stop. The pools can get crowded occasionally and local residents also tend to stop here frequently, especially on weekends.