Just beyond the east rim of the main caldera is this Kilauea Iki Crater. There's a great trail here that starts in rain forest on the rim and descends to the crater floor.
This crater was a lava lake in 1959. There's a fantastic old documentary about this eruption available on youtube.com. Go there are search for "The Eruption of Kilauea 1959-1960". There are 4 chapters.
