A little over half-mile past mile marker 18, mauka, on the Hana Highway you'll come to Wailua Valley State Wayside Park.
Most visitors breeze right by and never even realize it is there. The park provides perspectives of the Ke'anae Valley (a lower portion of the Ko'olau Gap in Haleakala's crater) and an overlook of Wailua Village. It's not a major attraction, but it's worth a stop for some great scenic views. After parking, take the stairs up to the lookout on your right. If you're interested, a paved overlook in another quarter-mile down the highway provides an even better look at Wailua town.