While you're in Hana make sure to take a moment to stop by Hana Bay where you'll find a large black sand beach. The black sand was formed as lava eroded slowly over time, eventually washing up around the bay.
Swimming is usually pretty good, but be sure to check with a local resident before jumping in. The Hana pier is located on the right side of the bay and offers a unique view of Hana town if you have a chance to walk out on it. The large hill at the far right end of the bay is Ka'uiki Hill. If you walk to the end of the road where the pier begins, you should be able to find a trail heading up and around the hill. If you follow it a while you can get some nice views of the Hana coastline, Hana town, and even visit a small red sand pocket beach about 200 yards into the hike. Sand can vary at the beach throughout the year, so don't expect much. The best treat along this hike is the view of Hana town with Haleakala in the background.