Into the mist...
It is important to stay between the cairns. Technically you aren't free to roam the crater at your leisure. There is a set path--follow the piles of rocks (aka Ahu) lining the crater. There's a reason the path exists--there are steam vents throughout the crater and some of the rocks near them could actually burn you! The vents are created from precipitation that seeps through the cracks in the earth and is boiled from the heat below. It would be like walking on a glacier, you want to avoid falling in a crack. Altho, these cracks don't seem as deep.

Kilauea Iki is a collapse crater (a smaller, younger crater) that's located inside the larger Kilauea Caldera, which is the summit crater of the Kilauea volcano. Essentially, Kilauea Iki is a feature within Kilauea, not a separate, independent volcano. Kilauea is the main volcano itself, a massive shield volcano, while Kilauea Iki is a specific, smaller crater on its surface.