Jennifer crafted a great itinerary for us--around three calderas, across Kilauea Iki, through the lava tube, and around the Sulphur Banks trail. All of these things are accessible in the park, but Jennifer puts everything in context: dates of eruptions, types of lava, the reasons why this amazing area looks like it does.
If you want more than the standard drive-by visit, I strongly suggest planning a day with VHG.