The coast trail leaves the right side of the parking lot at the Black Sand beach overlook and passes near an occasionally active blowhole, then winds along the desolate shore, on a black lava shelf out of reach of waves crashing below.
In the interest of full disclosure, we don’t really know how far the trail extends, since we’ve only gone 2 1/2 miles down the coast before turning back. There’s little shade and, while the scenery along the coast can be spectacular, it does get repetitive after awhile. Honestly, waves crashing against black lava, blowholes and lava arches are great, but after baking in the hot sun for an hour, it all seems more than enough. Turn back whenever you've had enough.
Waiananpanapana State Park, off the Hana Highway a few miles outside of Hana, has some interesting attractions besides the coast hike. There’s the Black Sand beach, of course. Most visitors pull in to the parking lot, take a picture or two from the overlook. They’ll walk down to the beach and, if adventurous, walk through the lava cave on the right side of the beach. A few may even go into the water if the sea is calm.
Slightly more adventurous types might take the short loop trail from the left of the parking lot to a freshwater cave - according to legend the unsuccessful hiding place for a Hawaiian princess.
Incidentally, be sure to bring a towel and take a refreshing dip in the cave after your coast hike!