My first visit. I hope to return before too long.
We stayed on the west coast near Captain Cook, up the road from Pebbles Beach. Ancient trails extend north and south from the beach, across lava flows from Mauna Loa. Lava flows are a dominant feature of Hawaii, which of course is still growing, although apparently there is a new baby island on the way in a few hundred thousand years...
Pu'uhonua O Honaunau National Historical Park. Wikipedia: "The historical park preserves the site where, up until the early 19th century, Hawaiians who broke a kapu (one of the ancient laws) could avoid certain death by fleeing to this place of refuge or puʻuhonua. The offender would be absolved by a priest and freed to leave. Defeated warriors and non-combatants could also find refuge here during times of battle. The grounds just outside the Great Wall that encloses the puʻuhonua were home to several generations of powerful chiefs."
Kilauea Iki Trail / Crater. An awesome hike across the floor of a crater that last erupted in 1959, right next door to the active crater at Kilauea. The native ʻōhiʻa lehua tree is trying its best to colonize every nook and cranny.
Makuala O'oma Trail. Fantastic trail through the cloud forest above Kona. The native hāpuʻu tree fern is abundant here, lending a Jurassic Park quality to the place. Invasive ginger plants are a real problem, though their flowers are pretty and fragrant.