In some places, the roof of the tube has collapsed, creating 'skylights' (and probably also why we're wearing helmets, ha ha). Deeper in the tunnel, it's totally dark -- but lit up with lights (except for a few minutes where they demonstrate how dark it really is without them).

After the lava tube, back to explore Hveragerði (staying in town for 2 nights, but never figuring out how to pronounce it). Not much traffic on the roads here -- although there can be lots of traffic back in Reykjavik -- especially during rush hour.