It is impossible to explore the ancient Hawaiian culture without running into the term kapu, which can be most easily understood as taboo. Ancient Hawaiians used the kapu system to enforce law and order, and there were numerous customs that invoked strict punishment as a consequence of violation. Transgressions could range from stepping on the shadow of an ali'i, or chief, to working the land during the makahiki, the fallow season, or fishing in forbidden waters, or even eating with a member of the opposite sex. The uses of the kapu were many, and the punishment was frequently death.
The one chance an offender might have to escape their death sentence was here at the Pu'uhonua, the place of refuge. If the offender managed to escape immediate execution and elude captors, their task was to reach this spot, the only spot on the Big Island where clemency could be given. No matter where the kapu was violated, refugees would risk their lives in the ocean or over harsh and jagged land to reach Pu'uhonua because the only alternative was execution.
The site's mana, or power, comes from the Hale o Keawe Heiau, a royal mausoleum that holds the remains of several generations of ali'i. This heiau is at the entrance to the Pu'uhonua, which is otherwise enclosed by the Great Wall, a true feat of labor. This wall reaches heights of 12 feet and averages 18 feet wide for its entire 950 feet length, and all of the stones are hand placed and dry set. The shore around the Pu'uhonua consists of jagged lava; between the wall and the shore, the sacred space was effectively isolated to all but the very holy and the very desperate. Inside the Pu'uhonua you'll have the opportunity to walk a footpath and see the sacred area, the remains of other heiau, spot a genuine kōnane board (a checkers-like game played with stones), and appreciate the Hale ō Keawe itself.
Outside of the Pu'uhonua sit the royal grounds, and there are several stops to make here as well. You'll see a reconstruction of Hale ō Keawe, the royal fishponds that were used for keeping and harvesting food for the ali'i, and several hālau, traditional structures made from ōhi'a wood and thatched pili grass.
Be sure to grab a pamphlet as you pay the entrance fee because it details a suggested walking route and has numbered stops for you to reference as you proceed. This really is a fascinating place, so do yourself a favor and budget plenty of time to appreciate it.
If you are looking to extend your day once you finish here, consider a stop at Pae'a, also known as Two Step, which is adjacent to Pu'uhonua O Hōnaunau National Historical Park. The area has excellent snorkeling right from the lava rock entrance, hence the name Two Step. And note that, while parking near Pae'a is $5 if you can't get a spot on the road, your $5 entrance fee to Pu'uhonua O Hōnaunau National Historical Park also buys you a parking spot just a five-minute walk away.