Reykjavik, Iceland: The slim platform I'm perching on dangles on wires out of a chimney at the top of an immense cavern.

I'm being lowered through the dome of a subterranean cathedral-like space. Above me, the volcanic crater is a small bright circle in a thin tube. Beside me rainwater runs down ripples of frozen lava and cascades into the quiet depths, gleaming in the spotlights from this repurposed window-cleaning rig.

The lights pick out rich hues on the wall – huge elemental murals in blue peacock rainbows and rich scarlet scorchmarks daubed by the Earth's fire.

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