The Hawai'ian Islands are of volcanic origin. There are almost no karst caves on the island, but a huge amount of lava tubes.
Hawai'i is sometimes called the highest mountain on Earth, as this shield volcano reaches from the ocean floor 4,000m below sea level to the top of Mauna Kea with 4,200m above sea level, which is more than 8,200m. This huge mountain is very flat, just about 4% slope, and the lava tends to calmly flow down this slope. An ideal situation for the formation of lava tubes.
The lava tubes on Hawai'i have been used as shelters and religious centres. Many of them are holy places, on private property or in a National Park. This makes it rather difficult, to go caving on Hawai'i. Some private owned caves can be visited.
The only real show cave was Thurston Lava Tube in Volcano National Park on Big Island. Unfortunately it was destroyed by an earthquake during an eruption in 2018 and will not be reopened. The best cave for tourists are now Ka'eleku Cavern in Hana on Maui, and Kazumura Cave near Hilo on Big Island. Of course there are numerous other small caves around, but they require good walking shoes.