North of Hana in Wai Anapana State Park on Maui, the Hana-Waianapanapa Coast Trail is an easy 6 mile hike along a flat coastal route. It runs along lava cliffs and through Lauhala forests. A good place to start is the Waianapanapa Campground north of Hana on SR31.
Note: Known for torrential rain and mud, even in campground.
Here are some notes on adventuring in Hawaii. First, unlike mainland forests, the tropical island forests can grow very dense and can mask dropoffs. Plus, the trails can be very wet and slick most of the year (December to February is the main rainy season, but expect rain all year round). Stay on the trail to avoid disorientation. Second, speaking of disorientation, be aware that most Hawaiian topographic maps use the Old Hawaiian Datum. When trying to use the latitude/longitude from those maps with a GPS unit, you will think you are 0.4 miles south/southeast of where you really are. Kind of important in a dense jungle. Third, the bacteria Leptospirosis is found in the local waters and mud. It causes flu like symptoms within 2-20 days of contact, and can be fatal if not treated with antibiotics. Fourth, when hiking about, walking sticks can be very helpful for stablity in the slick conditions, for probing mud hole depths and clearing webs of the tiny crab spider.
Overall, Hana-Waianapanapa Coast Trail is the 31st most popular hiking trail of all 45 hikes in Hawaii.