One of the top 3 "things to do" on Maui is the road to Hana. Hana is a small unremarkable town on the southeast coast of Maui so the attraction really is the one and only road to get there. From Pa'ia it hairpin-turns for 38 miles around the coast; hugging the steep hillsides, looping into valleys and then back overlooking the coast. The paved road is technically two-lane, except for the frequent single lane bridges and the sharp bends and other random stretches that are either marked one lane, or just require nerves of steel. Generally all the cars are driving to Hana in the morning and back in the afternoon so there isn't a lot of on-coming traffic, but if there is, it'll probably be a local driving a monsterized pick-up truck and he'll be driving fast and without any patience or consideration for the hordes of tourists clogging their one road.
The road takes you past rivers and waterfalls, small villages and pools, and the occasional fruit-stand and arboretum. And almost the whole outbound journey on your left is the ocean and on your right is a sheer cliff strewn with bromeliads and other exotic flowers. Although it's winter, everything is in bloom.
Choose your stops wisely amongst the many options to-walk-to-this-overlook or to hike-to-that-waterfall, or you'll find it's taken 8 or 10 hours to reach Hana (and remember the daylight lasts almost exactly 12 hours here) and the road peters out soon after Hana - the only road back is the one you took. There are no streetlights on the road from Hana, so think carefully if you want to drive back in the dark. It's a long, beautiful but surprisingly tiring drive - I'm glad there were two us to share the driving.
We did get to see one amazing phenomenon on our return, at one particularly scenic bend in the road, out there on the ocean was the clearest, strongest, most complete rainbow we've ever seen. Both "pots of gold" firmly planted on the 'treasure' of Maui ocean and beach and the full curve of the arc clearly visible. It was a magical moment.