Though drastically changed in recent months after the eruption of Kilauea, a visit to Hawaii isn't complete without marveling at Hawai'i Volcanoes National Park, home to the world's most active volcano and a World Heritage Site. The park is again re-open, albeit with a different and lava-less landscape.
Because of the recent earthquake, make sure to get up to date information and conditions on the park before you go! Though lava was no longer flowing at time of writing, this is still considered one of the most active volcanoes in the world.
Hawai'i Volcanoes National Park is on the island of Hawaii (AKA, the Big Island). Fly into Hilo or Kona International airports and book a rental car from the airport. Because of competition, good deals can be found. The drive from Kona is much longer than from Hilo, but quite pretty. If you take the southern route, stop at South Point Park, the southernmost point of the United States.