South of Kailua-Kona, and at the southern end of Kealakekua Bay is is a mouthful of syllables known as Pu'uhonua O Honaunau National Park, a.k.a., Place of Refuge. Though this is the most spectacular, similar places can be found throughout the Islands, where miscreants, vanquished combatants, and anyone else on the bad side of the the Ali'i (royals) could flee to avoid punsihment. When you're on an island and justice is a swift club, people hustle to get into prison.
The national park has many remnants from ancient times including the Great Wall from the 1500s, which is 1,000 feet long, 10-feet high and seven-feet thick. These days, especially on weekends, you'll find Hawaiians practicing traditional arts, like canoe making and weaving.
Also on site is Hale O Keawe, where the bones of some two-dozen Ali'i were interred. Adjacent to the park on the south is an ancient village site and a trail that goes for miles, some of it part of a huge cobblestone ramp, part of an old road. On the north side of the park is Two-Step, which offers some of the best snorkeling in the Hawaii, if you don't mind crowds on idyllic weekends.
You can spend a couple days exploring all the cool stuff at Kealakekua. Hawaii the Big Island Trailblazer has the deets, pages 96 to 104.