After spending a few days at Kona, we drove around the island to Volcanoes National Park . The drive down the coast was scenic (first photo below), and the volcano itself is unreal. Huge craters, vast plains of solidified lava, and sulfur fumes intermixed with lush vegetation. We saw it for the first time in the rain near dark, which made it even more impressive.
The next day we spent the entire day doing small to medium hikes of different parts of the park, including going across a crater and down to the water near where the lava was running into the ocean (you can see the steam in the third photo below -- yes, it's a live volcano!).