Going Down Under in Iceland

This is the entrance way to a lave tube, a cave created when the red hot lava briefly hardens around the outer skin while the centre core continues to flow. Eventually the flowing lava runs out and the tube, or tunnel is left. This is only a small one although it is still large enough to accommodate a couple of double-decker buses. I was not game to crawl through the end hole to see exactly how far is extended.

This is the entrance to Raufharholsvellir lava tube on the Reykjanes Peninsula. Pic by Natalie

This tube had collapsed in two places allowing light to blast into the dark, dripping space below.
It is enormous - probably four to five metres high and six to eight metres wide.
Parks department had constructed rough steps in parts of the tube so it was easier to negotiate the gloom.
I thought this would be maybe 80-100metres long - which is about as far as you can see here.
In fact it's more than 1.3 kilometres long - but dark.