Kaumana Caves are one lava tube (how's that for grammatically correct English?) from a 1881 Mauna Loa eruption. This lava flow threatened the town of Hilo until one of the princesses offered things (I can't remember what) to Pele, the Goddess of the volcano. The flow stopped a day later.
These caves are basically tubes in which lava flowed. They extend for a mile or so in either direction, and are usually rather large. There are sections were the ceiling gets low, so crawling is inevitable for a large person. This shot was taken by Andrew on our first trip in, and the caves were rather wet. You can see water coming down the tube, and this made for a wet hike, especially if you accidentally stepped into the 'river'. Oh, and they're pitch black too, so flashlights are mandatory.