I spent 2 nights at Volcano House. I arrived at 5pm and found that there was a park volunteer trip to a viewing site taking place right away. This is free with an optional donation. There were just 3 of us with a really knowledgeable and enthusiastic guide who told us about the plants (90% exclusive to Hawaii) and volcanic activity. We strolled about a mile as the sun set over the caldera. I learned such a lot and she told me about a night time lecture at the visitors centre. Again this was free and is held once a month so I was lucky.
The next day I did a great walk across 2 calderas. People were generous with their advice and I found great routes and had a lift along the road from a park ranger. I did the chain of craters drive to the coast. The lava wasn't flowing when I was there but I found seeing the lava bubbling in the caldera at night awesome (not a word I use often) and the sulphur and vapour rising freaky and unsettling. I highly recommend staying at Volcano House to get the full experience. The restaurant overlooks the caldera which glows red at night and steams all day with great views of the mountain when it's clear. I could have stayed longer.More