With a trailhead located the west end of the visitor center parking lot, the Sulphur Banks Trail is a popular and easily accessible hike for anyone visiting Hawai'i Volcanoes National Park. It's an easy way to follow up on some of the information you can gather at the visitor center: Stop in to watch the video, see the models that explain some of the geothermal activity in the area, and talk to a ranger. Then, without reparking, simply head west for this easy trail that provides a close-up perspective on the very, very active geology beneath your feet.
Five-hundred years ago, Kīlauea was a summit floating on an underground molten lake. As eruptions released lava to the surface, there was a corresponding decline in the support for that summit, and eventually the entire surface sank down and became the Kīlauea Caldera that we know and love today. The Sulphur Banks area sits in a transitional zone between the caldera and the ground that was left unaffected. This area is filled with steam from surface water that trickles down toward superheated rock, only to rise again as vapor. And, of course, there is the sulphur dioxide that rises from the magma beneath the caldera through fractures in the earth; this is the gas that gives the area its distinct odor, and it also discolors the rocks with easily perceptible yellow crystals.
The walk through the Sulphur Banks is either on an asphalt path or on a boardwalk, so it is ADA accessible and good for kids and families pushing strollers. It is absolutely imperative to stay on the path in this area; those who wander off risk penetrating the thin crusts of earth that hold scorching hot steam beneath. But because the boardwalk takes you to within a few feet of some of these vents, you don't really even need to leave the path for a closer look.
If the accessibility of the Sulphur Banks Trail is a positive for you, you may want to consider making this an out and back trip. If, on the other hand, you are able to handle a relatively level and straightforward but narrow dirt trail, returning via the Crater Rim Trail provides a significant change in scenery, some excellent views of the caldera, and a close look at additional steam vents. Simply cross Crater Rim Drive once you reach the end of the Sulphur Banks trail and continue to the Crater Rim Trail. Take a left to follow the trail through the dense rainforest for just a half mile back to the visitor center.