As you continue on Highway 31, beyond mile marker 29, you should see a pull out makai. Here you can view the Pokowai Sea Arch. The arch was formed when flowing lava from the volcano collided with the cold Pacific waters, creating an arch formation.
Take Highway 31 past Hana, past Kaupo. Around Mile Marker #29 the sea arch can be seen from the road - pullouts located near the shoreline are the safest spots to see and photograph this site.