I just got back from the big island last week! I took a bike tour of the Volcanoes National Park, which was a great way to see everything firsthand. I went with http://bikevolcano.com and we stopped at craters, walked through the Thurston lava tube and pedaled through the surrounding rainforest. You can also bike to where the live lava flow is and do a tour of the volcano winery. Definitely one of my favorite activities - make sure you have a full day to dedicate to it. about 6 years ago
I've hiked out to see the lava flow (Hilo side) and it was amazing. We hiked out late afternoon so were there for the sunset. It is a bit of a difficult hike back across the lava fields in the dark though.
try to find some steam caves too! They're awesome :) about 5 years ago
Frankly,I'd check the National Park web site to find out how much lava is flowing, and where. It can vary a lot. We were there for a week last January, and during our stay the lava stopped flowinginto the ocean, lessening the appeal of the boat tours. about 5 years ago